View Filing Data

Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2016	Aug. 02, 2016
Document and Entity Information
Entity Registrant Name	TC PIPELINES LP
Entity Central Index Key	0001075607
Document Type	10-Q
Document Period End Date	Jun. 30, 2016
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		65,937,080
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	Q2

CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Transmission revenues	$ 89	$ 85	$ 175	$ 172
Equity earnings (Note 4)	22	15	64	46
Operation and maintenance expenses	(12)	(13)	(22)	(24)
Property taxes	(5)	(5)	(10)	(11)
General and administrative	(2)	(1)	(4)	(4)
Depreciation	(22)	(21)	(43)	(42)
Financial charges and other (Note 14)	(16)	(16)	(33)	(29)
Net income	54	44	127	108
Net income attributable to non-controlling interests				7
Net income attributable to controlling interests	54	44	127	101
Net income attributable to controlling interest allocation
General Partner	3	2	5	3
Net income attributable to controlling interests	54	44	127	101
Common units
Net income attributable to controlling interest allocation
Limited partners	$ 50	$ 42	$ 121	$ 98
Net income per common unit (Note 8) - basic (in dollars per unit)	$ 0.76	$ 0.66	$ 1.86	$ 1.53
Net income per common unit (Note 8) - diluted (in dollars per unit)	$ 0.76	$ 0.66	$ 1.86	$ 1.53
Weighted average common units outstanding - basic (in units)	65.5	63.8	64.9	63.7
Weighted average common units outstanding - diluted (in units)	65.5	63.8	64.9	63.7
Common units outstanding, end of period (in units)	65.9	64.0	65.9	64.0
Class B units
Net income attributable to controlling interest allocation
Limited partners	$ 1		$ 1

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Net income	$ 54	$ 44	$ 127	$ 108
Other comprehensive income
Change in fair value of cash flow hedges (Note 12)	(1)		(3)	(1)
Comprehensive income	53	44	124	107
Comprehensive income attributable to non-controlling interests				7
Comprehensive income attributable to controlling interests	$ 53	$ 44	$ 124	$ 100

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Current Assets
Cash and cash equivalents	$ 40	$ 39
Accounts receivable and other (Note 13)	35	35
Distribution receivable from affiliate (Note 11)	4
Inventories	7	7
Total current assets	86	81
Equity investments (Note 4)	1,047	965
Plant, property and equipment (Net of $850 accumulated depreciation; 2015 - $811)	1,913	1,949
Goodwill	130	130
Other assets (Note 3)		1
Total assets	3,176	3,126
Current Liabilities
Accounts payable and accrued liabilities	26	32
Accounts payable to affiliates (Note 11)	5	5
Accrued interest	9	8
Current portion of long-term debt (Note 5)	15	14
Total current liabilities	55	59
Long-term debt (Notes 3 and 5)	1,938	1,889
Other liabilities	29	27
Total liabilities	2,022	1,975
Common units subject to rescission	83
Partners' Equity
General partner	25	25
Accumulated other comprehensive loss	(5)	(2)
Controlling interests	1,071	1,151
Total liabilities and partners' equity	3,176	3,126
Common units
Partners' Equity
Limited partner	955	1,021
Class B units
Partners' Equity
Limited partner	$ 96	$ 107

CONSOLIDATED BALANCE SHEET (Parenthetical) $ in Millions	Jun. 30, 2016 USD ($)
CONSOLIDATED BALANCE SHEETS
Accumulated depreciation	$ 850

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash Generated From Operations
Net income	$ 127	$ 108
Depreciation	43	42
Amortization of debt issue costs reported as interest expense (Note 3)	1	1
Equity allowance for funds used during construction		(1)
Change in operating working capital (Note 10)	3	1
Total cash generated from operations	170	151
Investing Activities
Acquisition of the remaining 30 percent interest in GTN		(264)
Capital expenditures	(18)	(12)
Other	2	(1)
Total investing activities	(171)	(258)
Financing Activities
Distributions paid to non-controlling interests		(9)
Common unit issuance, net		26
Common unit issuance subject to rescission, net (Note 7)	83
Equity contribution by the General Partner		2
Long-term debt issued, net of discount (Note 5)	205	424
Long-term debt repaid (Note 5)	(155)	(205)
Debt issuance costs		(3)
Total financing activities	2	125
Increase in cash and cash equivalents	1	18
Cash and cash equivalents, beginning of period	39	26
Cash and cash equivalents, end of period	40	44
Class B units
Financing Activities
Distributions paid (Note 7)	(12)
Common units and General Partner interest combined
Financing Activities
Distributions paid (Note 9)	(119)	(110)
Northern Border
Investing Activities
Cumulative distributions in excess of equity earnings	25	13
Great Lakes
Investing Activities
Cumulative distributions in excess of equity earnings	17	10
Investment in Great Lakes / Acquisition of PNGTS (Note 6)	(4)	$ (4)
Portland Natural Gas Transmission System
Cash Generated From Operations
Equity earnings in excess of cumulative distributions	(4)
Investing Activities
Investment in Great Lakes / Acquisition of PNGTS (Note 6)	$ (193)

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical)	Jun. 30, 2016	Apr. 01, 2015
GTN \| Transaction between entities under common control \| Former parent, TransCanada subsidiaries
Acquisitions
Interest acquired (as a percent)	30.00%	30.00%

CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY - 6 months ended Jun. 30, 2016 - USD ($)
shares in Millions, $ in Millions

Limited Partners

Common units

Limited Partners

Class B units

General Partner

Accumulated Other Comprehensive Loss

^[1]

Total

Partners' Equity at beginning of period at Dec. 31, 2015

$ 1,021

$ 107

$ 25

$ (2)

$ 1,151

Partners' Equity at beginning of period (in units) at Dec. 31, 2015

64.3

1.9

Increase (Decrease) in Partners' Equity

Net income

$ 121

$ 1

127

Other Comprehensive Loss

(3)

Common unit issuance subject to rescission, net (Note 7)

$ 81

Common unit issuance subject to rescission, net (Note 7) (in units)

1.6

Reclassification of common unit issuance subject to rescission, net (Note 7)

$ (81)

(2)

(83)

Reclassification of common unit issuance subject to rescission, net (Note 7) (in units)

(1.6)

Acquisition of PNGTS (Note 6)

$ (72)

(1)

(73)

Distributions

(115)

(12)

(4)

(131)

Partners' Equity at end of period at Jun. 30, 2016

$ 955

$ 96

$ 25

$ (5)

$ 1,071

Partners' Equity at end of period (in units) at Jun. 30, 2016

64.3

1.9

[1]

Losses related to cash flow hedges reported in Accumulated Other Comprehensive Loss and expected to be reclassified to Net Income in the next 12 months are estimated to be $2 million. These estimates assume constant interest rates over time; however, the amounts reclassified will vary based on actual value of interest rates at the date of settlement.

CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY (Parenthetical) $ in Millions	6 Months Ended
	Jun. 30, 2016 USD ($)
Losses related to cash flow hedges reported in Accumulated Other Comprehensive Loss
Losses expected to be reclassified to Net Income in the next 12 months	$ 2

ORGANIZATION	6 Months Ended
ORGANIZATION	Jun. 30, 2016
ORGANIZATION
ORGANIZATION	NOTE 1ORGANIZATION TC PipeLines, LP and its subsidiaries are collectively referred to herein as the Partnership. The Partnership was formed by TransCanada PipeLines Limited, a wholly owned subsidiary of TransCanada Corporation (TransCanada Corporation together with its subsidiaries collectively referred to herein as TransCanada), to acquire, own and participate in the management of energy infrastructure assets in North America. The Partnership owns its pipeline assets through three intermediate limited partnerships (ILPs), TC GL Intermediate Limited Partnership, TC PipeLines Intermediate Limited Partnership and TC Tuscarora Intermediate Limited Partnership.

SIGNIFICANT ACCOUNTING POLICIES	6 Months Ended
SIGNIFICANT ACCOUNTING POLICIES	Jun. 30, 2016
SIGNIFICANT ACCOUNTING POLICIES
SIGNIFICANT ACCOUNTING POLICIES	NOTE 2SIGNIFICANT ACCOUNTING POLICIES The accompanying financial statements and related notes have been prepared in accordance with United States generally accepted accounting principles (GAAP) and amounts are stated in U.S. dollars. The results of operations for the three and six months ended June 30, 2016 and 2015 are not necessarily indicative of the results that may be expected for the full fiscal year. The accompanying financial statements should be read in conjunction with the financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2015. That report contains a more comprehensive summary of the Partnership’s significant accounting policies. In the opinion of management, the accompanying financial statements contain all of the appropriate adjustments, all of which are normally recurring adjustments unless otherwise noted, and considered necessary to present fairly the financial position of the Partnership, the results of operations and cash flows for the respective periods. Our significant accounting policies are consistent with those disclosed in our Annual Report on Form 10-K for the year ended December 31, 2015, except as described in Note 3, Accounting Pronouncements. Use of Estimates The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Although management believes these estimates are reasonable, actual results could differ from these estimates.

ACCOUNTING PRONOUNCEMENTS

6 Months Ended

Jun. 30, 2016

ACCOUNTING PRONOUNCEMENTS

ACCOUNTING PRONOUNCEMENTS

NOTE 3ACCOUNTING PRONOUNCEMENTS

Effective January 1, 2016

Consolidation

In February 2015, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2015-02 “Consolidation (Topic 810),” an amendment of previously issued guidance on consolidation. This updated guidance requires that an entity evaluate whether it should consolidate certain legal entities. All legal entities are subject to reevaluation under the revised consolidation model. This guidance became effective beginning January 1, 2016 and was applied retrospectively to all financial statements presented. The application of this guidance did not result in any change to the Partnership’s consolidation conclusions. Refer to Note 17, Variable Interest Entities.

Imputation of interest

In April 2015, the FASB issued ASU No. 2015-03 “Interest — Imputation of Interest (Subtopic 835-30),” an amendment of previously issued guidance on imputation of interest. This updated guidance requires debt issuance costs be presented in the balance sheet as a direct deduction from the carrying amount of debt liabilities, consistent with debt discount or premiums. In addition, amortization of debt issuance costs should be reported as interest expense. The recognition and measurement for debt issuance costs would not be affected. This guidance is effective from January 1, 2016 and was applied retrospectively resulting in a reclassification of debt issuance costs previously recorded in other assets to an offset of their respective debt liabilities on the Partnership’s consolidated balance sheet. Amortization of debt issuance costs was reported as interest expense in all periods presented in the Partnership’s consolidated statement of income.

As a result of the application of ASU No. 2015-03 and similar to the presentation of debt discounts, debt issuance costs of $7 million at December 31, 2015 previously reported as other assets in the balance sheet were reclassified as an offset against their respective debt liabilities.

Earnings per share

In April 2015, the FASB issued ASU No. 2015-06 “Earnings Per Share (Topic 260),” an amendment of previously issued guidance on earnings per share (EPS) as it is being calculated by master limited partnerships. This updated guidance specifies that for purposes of calculating historical EPS under the two-class method, the earnings (losses) of a transferred business before the date of a dropdown transaction should be allocated entirely to the general partner interest, and previously reported EPS of the limited partners would not change as a result of a dropdown transaction. Qualitative disclosures about how the rights to the earnings (losses) differ before and after the dropdown transaction occurs are also required. This guidance became effective from January 1, 2016 and applies to all dropdown transactions requiring recast. The retrospective application of this guidance did not have a material impact on the Partnership’s consolidated financial statements as our current accounting policy is consistent with the new guidance.

Business combinations

In September 2015, the FASB issued ASU No. 2015-16 “Business Combinations (Topic 805),” which replaces the requirement that an acquirer in a business combination account for measurement period adjustments retrospectively with a requirement that an acquirer recognize adjustments to the provisional amounts that are identified during the measurement period in the reporting period in which the adjustment amounts are determined. The amended guidance requires that the acquirer record, in the same period’s financial statements, the effect on earnings of changes in depreciation, amortization, or other income effects, if any, as a result of the change to the provisional amounts, calculated as if the accounting had been completed at the acquisition date. The new guidance is effective January 1, 2016 and was applied prospectively. The application of this guidance did not have a material impact on the Partnership’s consolidated financial statements.

Future accounting changes

Revenue from contracts with customers

In May 2014, the FASB issued ASU No. 2014-09 “Revenue from Contracts with Customers (Topic 606).” This guidance supersedes the revenue recognition requirements in Topic 605, Revenue Recognition and most industry-specific guidance. This new guidance requires that an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. On July 9, 2015, the FASB voted to defer the effective date by one year to December 15, 2017 for annual reporting periods beginning after that date. The FASB also voted to permit early adoption of the standard, but not before the original effective date of December 15, 2016. This new guidance, once effective, allows two methods in which the amendment can be applied: (1) retrospectively to each prior reporting period presented, or (2) retrospectively with the cumulative effect recognized at the date of initial application. This guidance supersedes the current revenue recognition requirements and most industry-specific guidance. The core principle relating to the new guidance requires that an entity recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. To achieve the core principle, a five step process is required:

Identify the contract with the customer

Identify the performance obligations in the contract

Determine the transaction price

Allocate the transaction price to the performance obligations

Recognize revenue when (or as) each performance obligations is satisfied

The new guidance also specifies the accounting for some costs to obtain or fulfill a contract, as well as enhanced disclosure requirements. The Partnership is currently identifying existing customer contracts or groups of contracts that are within the scope of the new guidance and that will require an assessment in order to determine any impact on its consolidated financial statements.

Leases

In February 2016, the FASB issued ASU No. 2016-03 “Leases (Topic 842).” The new guidance requires lessees to recognize most leases, including operating leases, on the balance sheet as lease assets and lease liabilities. In addition, lessees will be required to reassess assumptions associated with existing leases as well as to provide expanded qualitative and quantitative disclosures. The new standard does not make extensive changes to lessor accounting. The new guidance is effective January 1, 2019 and will be applied using a modified retrospective approach. The Partnership is currently identifying existing lease agreements that are within the scope of the new guidance that may have an impact on its consolidated financial statements.

Equity method and joint ventures

In March 2016, the FASB issued ASU No. 2016-07 “Investments — Equity Method and Joint Ventures (Topic 323)” that simplifies the transition to equity method accounting. The new guidance eliminates the requirement to retroactively apply the equity method of accounting when an increase in ownership interest in an investment qualifies for equity method accounting. This new guidance is effective January 1, 2017 and will be applied prospectively. The Partnership does not expect the adoption of this new standard to have a material impact on its consolidated financial statements.

EQUITY INVESTMENTS

6 Months Ended

Jun. 30, 2016

EQUITY INVESTMENTS

EQUITY INVESTMENTS

NOTE 4EQUITY INVESTMENTS

Northern Border, Great Lakes and Portland Natural Gas Transmission System (PNGTS) are regulated by FERC and are operated by subsidiaries of TransCanada. The Partnership uses the equity method of accounting for its interests in its equity investees. The Partnership’s equity investments are held through our ILPs that are considered to be variable interest entities (VIEs) . Refer to Note 3, Accounting Pronouncements and Note 17, Variable Interest Entities.

	Ownership		Equity Earnings from Unconsolidated Affiliates				Investments in Unconsolidated Affiliates
	Interest at		Three months		Six Months
(unaudited)	June 30,		ended June 30,		ended June 30,		June 30,	December 31,
(millions of dollars)	2016		2016	2015	2016	2015	2016	2015

Northern Border (a)	50	%	16	15	34	34	455	480
Great Lakes	46.45	%	4	—	19	12	472	485
PNGTS (b)	49.90	%	2	—	11	—	120	—

			22	15	64	46	1,047	965

(a)

Equity earnings from Northern Border is net of the 12-year amortization of a $10 million transaction fee paid to the operator of Northern Border at the time of the Partnership’s additional 20 percent interest acquisition in April 2006.

(b)

On January 1, 2016, the Partnership acquired a 49.9 percent interest in PNGTS (Refer to Note 6). For the three and six months ended June 30, 2016, the Partnership recorded no undistributed earnings from PNGTS.

Northern Border

The Partnership did not have undistributed earnings from Northern Border for the three and six months ended June 30, 2016 and 2015.

The summarized financial information for Northern Border is as follows:

(unaudited)
(millions of dollars)	June 30, 2016		December 31, 2015

ASSETS
Cash and cash equivalents	16		27
Other current assets	34		33
Plant, property and equipment, net	1,108		1,124
Other assets (a)	15		16

	1,173		1,200


LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	40		39
Deferred credits and other	27		26
Long-term debt, including current maturities, net (a)	429		409
Partners’ equity
Partners’ capital	679		728
Accumulated other comprehensive loss	(2	)	(2	)

	1,173		1,200

(a)

As a result of the application of ASU No. 2015-03 and similar to the presentation of debt discounts, debt issuance costs of $2 million at December 31, 2015 previously reported as other assets in the balance sheet were reclassified as an offset against their respective debt liabilities.

	Three months ended				Six months ended
(unaudited)	June 30,				June 30,
(millions of dollars)	2016		2015		2016		2015

Transmission revenues	70		69		144		144
Operating expenses	(18	)	(18	)	(35	)	(34	)
Depreciation	(15	)	(14	)	(29	)	(29	)
Financial charges and other	(6	)	(6	)	(11	)	(11	)

Net income	31		31		69		70

Great Lakes

The Partnership made an equity contribution to Great Lakes of $4 million in the first quarter of 2016. This amount represents the Partnership’s 46.45 percent share of a $9 million cash call from Great Lakes to make a scheduled debt repayment.

The Partnership did not have undistributed earnings from Great Lakes for the three and six months ended June 30, 2016 and 2015.

The summarized financial information for Great Lakes is as follows:

(unaudited)
(millions of dollars)	June 30, 2016	December 31, 2015

ASSETS
Current assets	53	86
Plant, property and equipment, net	721	727

	774	813


LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	29	31
Long-term debt, including current maturities, net (a)	288	297
Partners’ equity	457	485

	774	813

(a)

The application of ASU No. 2015-03 did not have a material effect on Great Lakes’ financial statements.

	Three months ended				Six months ended
(unaudited)	June 30,				June 30,
(millions of dollars)	2016		2015		2016		2015

Transmission revenues	36		28		97		76
Operating expenses	(15	)	(14	)	(30	)	(25	)
Depreciation	(7	)	(7	)	(14	)	(14	)
Financial charges and other	(5	)	(6	)	(11	)	(12	)

Net income	9		1		42		25

DEBT AND CREDIT FACILITIES

6 Months Ended

Jun. 30, 2016

DEBT AND CREDIT FACILITIES

DEBT AND CREDIT FACILITIES

NOTE 5DEBT AND CREDIT FACILITIES

(unaudited) (millions of dollars)	June 30, 2016	December 31, 2015	Weighted Average Interest Rate for the Six Months Ended June 30, 2016

TC PipeLines, LP Senior Credit Facility due 2017	250	200	1.69	%
TC PipeLines, LP 2013 Term Loan Facility due 2018	500	500	1.69	%
TC PipeLines, LP 2015 Term Loan Facility due 2018	170	170	1.58	%
TC PipeLines, LP 4.65% Unsecured Senior Notes due 2021	350	350	4.65	%(b)
TC PipeLines, LP 4.375% Unsecured Senior Notes due 2025	350	350	4.375	%(b)
GTN 5.29% Unsecured Senior Notes due 2020	100	100	5.29	%(b)
GTN 5.69% Unsecured Senior Notes due 2035	150	150	5.69	%(b)
GTN Unsecured Term Loan Facility due 2019	65	75	1.38	%
Tuscarora Unsecured Term Loan due 2019	10	—	1.57	%
Tuscarora 3.82% Series D Senior Notes due 2017	16	16	3.82	%(b)

	1,961	1,911
Less: unamortized debt issuance costs and debt discount (a)	8	8
Less: current portion	15	14

	1,938	1,889

(a)

(b)

Fixed interest rate

The Partnership’s Senior Credit Facility consists of a $500 million senior revolving credit facility with a banking syndicate, maturing November 20, 2017, under which $250 million was outstanding at June 30, 2016 (December 31, 2015 - $200 million), leaving $250 million available for future borrowing.

After hedging activity, the interest rate incurred on the 2013 Term Loan Facility averaged 2.31 percent and 2.25 percent for the three and six months ended June 30, 2016, respectively (2015 — 1.84 percent). Prior to hedging activities, the LIBOR-based interest rate was 1.71 percent at June 30, 2016 (December 31, 2015 — 1.50 percent).

The 2013 Term Loan Facility and the 2015 Term Loan Facility (Term Loan Facilities) and the Senior Credit Facility require the Partnership to maintain a certain leverage ratio (debt to adjusted cash flow [net income plus cash distributions received, extraordinary losses, interest expense, expense for taxes paid or accrued, and depreciation and amortization expense less equity earnings and extraordinary gains]) no greater than:

5.50 to 1.00 for the quarters ending June 30, 2016 to September 30, 2016;

5.00 to 1.00 for the quarter ending December 31, 2016 and each subsequent fiscal quarter, except for the fiscal quarter and the two following fiscal quarters in which one or more acquisitions has been executed, in which case the leverage ratio is to be no greater than 5.50 to 1.00.

The leverage ratio was 4.37 to 1.00 as of June 30, 2016.

GTN’s Unsecured Senior Notes, along with GTN’s Unsecured Term Loan Facility contain a covenant that limits total debt to no greater than 70 percent of GTN’s total capitalization. GTN’s total debt to total capitalization ratio at June 30, 2016 was 43.7 percent.

On April 29, 2016, Tuscarora entered into a $9.5 million unsecured variable rate term loan facility which requires yearly principal payments until its maturity on April 29, 2019. The variable interest is based on LIBOR plus an applicable margin and was 1.59 percent at June 30, 2016.

Tuscarora’s Series D Senior Notes, which require yearly principal payments until maturity, are secured by Tuscarora’s transportation contracts, supporting agreements and substantially all of Tuscarora’s property. The note purchase agreements contain certain provisions that include, among other items, limitations on additional indebtedness and distributions to partners. The Series D Senior Notes contain a covenant that limits total debt to no greater than 45 percent of Tuscarora’s total capitalization. Tuscarora’s total debt to total capitalization ratio at June 30, 2016 was 24 percent. Additionally, the Series D Senior Notes require Tuscarora to maintain a Debt Service Coverage Ratio (cash available from operations divided by a sum of interest expense and principal payments) of greater than 3.00 to 1.00. The ratio was 4.57 to 1.00 as of June 30, 2016.

At June 30, 2016, the Partnership was in compliance with its financial covenants, in addition to the other covenants which include restrictions on entering into mergers, consolidations and sales of assets, granting liens, material amendments to the Third Amended and Restated Agreement of Limited Partnership (Partnership Agreement), incurring additional debt and distributions to unitholders.

The principal repayments required of the Partnership on its debt are as follows:

(unaudited)
(millions of dollars)

2016		4
2017		273
2018		691
2019		43
2020		100
Thereafter		850

		1,961

ACQUISITION

6 Months Ended

Jun. 30, 2016

ACQUISITION

ACQUISITION

NOTE 6ACQUISITION

PNGTS Acquisition

On January 1, 2016, the Partnership acquired a 49.9 percent interest in PNGTS from a subsidiary of TransCanada (PNGTS Acquisition). The total purchase price of the PNGTS Acquisition was $228 million and consisted of $193 million in cash (including the final purchase price adjustment of $5 million) and the assumption of $35 million in proportional PNGTS debt.

The Partnership funded the cash portion of the transaction using proceeds received from our ATM Program and additional borrowings under our Senior Credit Facility. The purchase agreement provides for additional payments to TransCanada ranging from $5 million up to a total of $50 million if pipeline capacity is expanded to various thresholds during the fifteen year period following the date of closing.

The acquisition was accounted for as a transaction between entities under common control, whereby the equity investment in PNGTS was recorded at TransCanada’s carrying value.

The net purchase price was allocated as follows:

(unaudited) (millions of dollars)
Net Purchase Price (a)		193
Less: TransCanada’s carrying value of PNGTS’ net assets at January 1, 2016		120

Excess purchase price (b)		73

(a)

Total purchase price of $228 million less the assumption of $35 million of proportional PNGTS debt by the Partnership.

(b)

The excess purchase price of $73 million was recorded as a reduction in Partners’ Equity.

PARTNERS' EQUITY	6 Months Ended
PARTNERS' EQUITY	Jun. 30, 2016
PARTNERS' EQUITY
PARTNERS' EQUITY	NOTE 7PARTNERS’ EQUITY ATM equity issuance program In the six months ended June 30, 2016, we issued 1,619,631 common units under our ATM program generating net proceeds of approximately $81 million, plus $2 million from the General Partner to maintain its effective two percent interest. The commissions to our sales agents for the six months ended June 30, 2016 were approximately $823,000. The net proceeds were used for general partnership purposes. On July 29, 2016, we filed a new shelf registration with the Securities Exchange Commission (SEC) to register an additional $400 million of common units. On August 2, 2016, we requested accelerated effectiveness of the amended shelf registration statement. Common unit issuance subject to rescission On July 17, 2014, the SEC declared effective a registration statement (the Registration Statement) that we had filed to cover sales of Common Units under our ATM program. On February 26, 2016, at the time of the filing of the 2015 Form 10-K, we believed that the Partnership continued to be eligible to use the effective Registration Statement to sell Common Units under our ATM program. However, we have been advised by the SEC on June 23, 2016 that as a result of the untimely filing of an employee-related Form 8-K on October 28, 2015, which was not filed via EDGAR until 6:02 p.m. Eastern Time (32 minutes after the 5:30 p.m. Eastern Time cutoff), the Partnership was ineligible to use the Registration Statement after the filing of the 2015 Form 10-K. Because the Partnership was ineligible to continue using the Registration Statement following the filing of the 2015 Form 10-K, it is possible that the sales of an aggregate 1,619,631 Common Units under the Registration Statement (the ATM Common Units), which were sold between March 8, 2016 and May 19, 2016 at per Common Unit prices ranging from $47.00 to $54.95, may be deemed to have been unregistered sales of securities. If it is determined that persons who purchased the ATM Common Units from the Partnership after February 26, 2016, purchased such Common Units in an offering deemed to be unregistered, then to the extent there may have been a violation of federal securities laws such persons may be entitled to rescission rights, pursuant to which they could be entitled to recover the amount paid for such ATM Common Units, plus interest (based on the statutory rate under applicable state law), less the amount of any distributions. If such investor has sold any of the ATM Common Units purchased by the investor, then the investor would be entitled to recover the difference between the amount paid for such ATM Common Units and the amount at which such ATM Common Units were sold, assuming the investor’s ATM Common Units were sold at a loss, plus interest and less the amount of any distributions. If all of the investors who purchased the ATM Common Units from the Partnership after February 26, 2016 continue to own all of the ATM Common Units and were to demand rescission of their purchases, and such investors were in fact found to be entitled to such rescission, then we would be obligated to repay approximately $82,334,015, plus interest, less the amount of any distributions. The Securities Act generally requires that any claim brought for a violation of Section 5 of the Securities Act be brought within one year of the violation. As a result, at June 30, 2016, the Partnership classified all the 1.6 million common units issued under its ATM program after February 26, 2016 up to and including June 30, 2016, which may be subject to rescission rights, outside of equity given the potential redemption feature which is not within the control of the Partnership. These units are treated as outstanding for financial reporting purposes. The total amount transferred outside of equity was approximately $83 million which includes interest and less distributions paid and includes our General Partner’s share to maintain its effective two percent interest. Class B units issued to TransCanada The Class B Units we issued on April 1, 2015 to finance a portion of the 2015 GTN Acquisition represent a limited partner interest in us and entitle TransCanada to an annual distribution based on 30 percent of GTN’s annual distributions as follows: (i) 100 percent of distributions above $20 million through March 31, 2020; and (ii) 25 percent of distributions above $20 million thereafter. For the year ending December 31, 2016, the Class B units’ equity account will be increased by the excess of 30 percent of GTN’s distributions over the annual threshold of $20 million until such amount is declared for distribution and paid in the first quarter of 2017. During the six months ended June 30, 2016, 30 percent of GTN’s total distributable cash flow was $21 million. As a result of exceeding the $20 million threshold, the Class B units’ equity account was increased by $1 million (Refer to Note 8). For the year ended December 31, 2015, the Class B distribution was $12 million and was declared and paid in the first quarter of 2016.

NET INCOME PER COMMON UNIT

6 Months Ended

Jun. 30, 2016

NET INCOME PER COMMON UNIT

NET INCOME PER COMMON UNIT

NOTE 8NET INCOME PER COMMON UNIT

Net income per common unit is computed by dividing net income attributable to controlling interests, after deduction of amounts attributable to the General Partner and Class B units, by the weighted average number of common units outstanding.

The amounts allocable to the General Partner equals an amount based upon the General Partner’s effective two percent general partner interest, plus an amount equal to incentive distributions. Incentive distributions are paid to the General Partner if quarterly cash distributions on the common units exceed levels specified in the Partnership Agreement.

The amount allocable to the Class B units in 2016 will equal an amount based upon 30 percent of GTN’s distributable cash flow during the year ending December 31, 2016 less $20 million (2015 – less $15 million).

Net income per common unit was determined as follows:

	Three months ended						Six months ended
(unaudited)	June 30,						June 30,
(millions of dollars, except per common unit amounts)	2016			2015			2016			2015

Net income attributable to controlling interests	54			44			127			101
Net income attributable to the General Partner	(1		)	(1		)	(2		)	(2		)
Incentive distributions allocated to the General Partner (a)	(2		)	(1		)	(3		)	(1		)
Net income attributable to the Class B units (b)	(1		)	—			(1		)	—

Net income allocated to common units	50			42			121			98

Weighted average common units outstanding (millions) — basic and diluted	65.5		(c)	63.8			64.9		(c)	63.7
Net income per common unit — basic and diluted	$	0.76		$	0.66		$	1.86		$	1.53

(a)

Under the terms of the Partnership Agreement, for any quarterly period, the participation of the incentive distribution rights (IDRs) is limited to the available cash distributions declared. Accordingly, incentive distributions allocated to the General Partner are based on the Partnership’s available cash during the current reporting period, but declared and paid in the subsequent reporting period.

(b)

As discussed in Note 7, the Class B units entitle TransCanada to a distribution which is an amount based on 30 percent of GTN’s distributions after achieving certain annual thresholds. The distribution will be payable in the first quarter with respect to the prior year’s distributions. Consistent with the application of Accounting Standards Codification (ASC) Topic 260 — “Earnings per share”, the Partnership allocated a portion of net income attributable to controlling interest to the Class B units upon 30 percent of GTN’s total distributable cash flows exceeding $20 million for the year ending December 31, 2016. During the six months ended June 30, 2016, 30 percent of GTN’s total distributable cash flow was $21 million. As a result of exceeding the $20 million threshold, $1 million of net income attributable to controlling interests was allocated to the Class B units (Refer to Note 7). During the same period in 2015, no allocation was made to the Class B units as the threshold level of $15 million for the nine month period ending December 31, 2015 had not been exceeded.

(c)

Includes the common units subject to rescission. These units are treated as outstanding for financial reporting purposes (Refer to Note 7).

CASH DISTRIBUTIONS	6 Months Ended
CASH DISTRIBUTIONS	Jun. 30, 2016
CASH DISTRIBUTIONS
CASH DISTRIBUTIONS	NOTE 9CASH DISTRIBUTIONS In the three and six months ended June 30, 2016, the Partnership distributed $0.89 and $1.78 per common unit, respectively (2015 — $0.84 and $1.68 per common unit) for a total of $60 million and $119 million, respectively (2015 - $55 million and $110 million). The distributions paid in the three and six months ended June 30, 2016 included an IDR payment to the General Partner of approximately $1 million and $2 million, respectively (2015 - $0.3 million and $0.6 million).

CHANGE IN OPERATING WORKING CAPITAL

6 Months Ended

Jun. 30, 2016

CHANGE IN OPERATING WORKING CAPITAL

CHANGE IN OPERATING WORKING CAPITAL

NOTE 10CHANGE IN OPERATING WORKING CAPITAL

(unaudited)	Six months ended June 30,
(millions of dollars)	2016	2015

Change in accounts receivable and other	—	4
Change in accounts payable and accrued liabilities (a)	2	(2	)
Change in accounts payable to affiliates	—	(5	)
Change in accrued interest	1	4

Change in operating working capital	3	1

(a)

The accrual of $10 million for the construction of GTN’s Carty Lateral in December 31, 2015 was paid during the first quarter 2016. Accordingly, the payment was reported as capital expenditures in our cash flow statement during the current period.

RELATED PARTY TRANSACTIONS

6 Months Ended

Jun. 30, 2016

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS

NOTE 11RELATED PARTY TRANSACTIONS

The Partnership does not have any employees. The management and operating functions are provided by the General Partner. The General Partner does not receive a management fee in connection with its management of the Partnership. The Partnership reimburses the General Partner for all costs of services provided, including the costs of employee, officer and director compensation and benefits, and all other expenses necessary or appropriate to the conduct of the business of, and allocable to, the Partnership. Such costs include (i) overhead costs (such as office space and equipment) and (ii) out-of-pocket expenses related to the provision of such services. The Partnership Agreement provides that the General Partner will determine the costs that are allocable to the Partnership in any reasonable manner determined by the General Partner in its sole discretion. Total costs charged to the Partnership by the General Partner were $1 million and $2 million for the three and six months ended June 30, 2016, respectively. Total costs charged to the Partnership by the General Partner were $1 million for both the three and six months ended June 30, 2015.

As operator of our pipelines, TransCanada’s subsidiaries provide capital and operating services to our pipeline systems. TransCanada’s subsidiaries incur costs on behalf of our pipeline systems, including, but not limited to, employee salary and benefit costs, and property and liability insurance costs.

Capital and operating costs charged to our pipeline systems for the three and six months ended June 30, 2016 and 2015 by TransCanada’s subsidiaries and amounts payable to TransCanada’s subsidiaries at June 30, 2016 and December 31, 2015 are summarized in the following tables:

	Three months ended		Six months ended
(unaudited)	June 30,		June 30,
(millions of dollars)	2016	2015	2016	2015

Capital and operating costs charged by TransCanada’s subsidiaries to:
Great Lakes (a)	7	8	14	14
Northern Border (a)	9	9	15	16
PNGTS (a), (c)	2	—	4	—
GTN (a), (b)	7	8	13	14
Bison (d)	1	1	—	2
North Baja	1	2	2	3
Tuscarora	1	1	2	2
Impact on the Partnership’s net income:
Great Lakes	3	3	6	6
Northern Border	3	4	6	7
PNGTS (c)	1	—	2	—
GTN (b)	6	7	11	11
Bison	1	1	2	2
North Baja	1	1	2	2
Tuscarora	1	1	2	2

(unaudited)
(millions of dollars)	June 30, 2016	December 31, 2015

Net amounts payable to TransCanada’s subsidiaries is as follows:
Great Lakes (a)	3	3
Northern Border (a)	3	5
PNGTS (a)	1	—
GTN	3	3
Bison	1	—
North Baja	—	—
Tuscarora	1	1

(a)

Represents 100 percent of the costs.

(b)

In April 2015, the Partnership acquired the remaining 30 percent interest in GTN.

(c)

In January 2016, the Partnership acquired 49.9 percent interest in PNGTS.

(d)

Net of proceeds of $1 million from the sale of excess pipe (at cost) to an affiliate.

Great Lakes earns transportation revenues from TransCanada and its affiliates, some of which are provided at discounted rates and some of which are at maximum recourse rates. Great Lakes earned $23 million and $69 million of transportation revenues under these contracts for the three and six months ended June 30, 2016, respectively (2015 - $18 million and $47 million). These amounts represent 64 percent and 71 percent of total revenues earned by Great Lakes for the three and six months ended June 30, 2016, respectively (2015 — 63 percent and 62 percent). Great Lakes also earned $1 million of affiliated rental revenue for the three and six months ended June 30, 2016 (2015 — $1 million).

Accordingly, revenue from TransCanada and its affiliates of $10 million and $32 million are included in the Partnership’s equity earnings from Great Lakes for the three and six months ended June 30, 2016, respectively (2015 - $8 million and $22 million). At June 30, 2016, $9 million was included in Great Lakes’ receivables in regards to the transportation contracts with TransCanada and its affiliates (December 31, 2015 - $17 million).

Effective November 1, 2014, Great Lakes executed contracts with an affiliate, ANR Pipeline Company (ANR), to provide firm service in Michigan and Wisconsin. These contracts were at the maximum FERC authorized rate and were intended to replace historical contracts. On December 3, 2014, the FERC accepted and suspended Great Lakes’ tariff records to become effective May 3, 2015, subject to refund. On February 2, 2015, FERC issued an Order granting a rehearing and clarification request submitted by Great Lakes, which allowed additional time for FERC to consider Great Lakes’ request. Following extensive discussions with numerous shippers and other stakeholders, on April 20, 2015, ANR filed a settlement with FERC that included an agreement by ANR to pay Great Lakes the difference between the historical and maximum rates (ANR Settlement). Great Lakes provided service to ANR under multiple service agreements and rates through May 3, 2015 when Great Lakes’ tariff records became effective and subject to refund. Great Lakes deferred an approximate $9 million of revenue related to services performed in 2014 and approximately $14 million of additional revenue related to services performed through May 3, 2015 under such agreements. On October 15, 2015, FERC accepted and approved the ANR Settlement. As a result, Great Lakes recognized the deferred transportation revenue of approximately $23 million in the fourth quarter of 2015.

On June 16, 2016, PNGTS declared its second quarter 2016 distribution of $8 million, of which the Partnership received its 49.9 percent share or $4 million on July 18, 2016.

FAIR VALUE MEASUREMENTS

6 Months Ended

Jun. 30, 2016

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS

NOTE 12FAIR VALUE MEASUREMENTS

(a) Fair Value Hierarchy

Under ASC 820, Fair Value Measurements and Disclosures, fair value measurements are characterized in one of three levels based upon the inputs used to arrive at the measurement. The three levels of the fair value hierarchy are as follows:

Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that we have the ability to access at the measurement date.

Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly.

Level 3 inputs are unobservable inputs for the asset or liability.

When appropriate, valuations are adjusted for various factors including credit considerations. Such adjustments are generally based on available market evidence. In the absence of such evidence, management’s best estimate is used.

(b) Fair Value of Financial Instruments

The carrying value of cash and cash equivalents, accounts receivable and other, accounts payable and accrued liabilities, accounts payable to affiliates and accrued interest approximate their fair values because of the short maturity or duration of these instruments, or because the instruments bear a variable rate of interest or a rate that approximates current rates. The fair value of the Partnership’s debt is estimated by discounting the future cash flows of each instrument at estimated current borrowing rates. The fair value of interest rate derivatives is calculated using the income approach, which uses period-end market rates and applies a discounted cash flow valuation model.

Long-term debt is recorded at amortized cost and classified in Level 2 of the fair value hierarchy for fair value disclosure purposes. Interest rate derivative assets and liabilities are classified in Level 2 for all periods presented where the fair value is determined by using valuation techniques that refer to observable market data or estimated market prices. The estimated fair value of the Partnership’s debt as at June 30, 2016 and December 31, 2015 was $1,994 million and $1,873 million, respectively.

The ATM Common units which may be subject to rescission rights, as discussed more fully in Note 7, were measured using the original issuance price, plus statutory interest and less any distributions paid. This fair value measurement is classified as Level 2.

Market risk is the risk that changes in market interest rates may result in fluctuations in the fair values or cash flows of financial instruments. The Partnership’s floating rate debt is subject to LIBOR benchmark interest rate risk. The Partnership uses interest rate derivatives to manage its exposure to interest rate risk. We regularly assess the impact of interest rate fluctuations on future cash flows and evaluate hedging opportunities to mitigate our interest rate risk.

The interest rate swaps are structured such that the cash flows of the derivative instruments match those of the variable rate of interest on the 2013 Term Loan Facility. The Partnership hedged interest payments on the variable-rate 2013 Term Loan Facility with interest rate swaps maturing July 1, 2018, at a weighted average fixed interest rate of 2.31 percent. At June 30, 2016, the fair value of the interest rate swaps accounted for as cash flow hedges was a liability of $5 million (both on a gross and net basis) (December 31, 2015 - $1 million). The Partnership did not record any amounts in net income related to ineffectiveness for interest rate hedges for the three and six months ended June 30, 2016 and 2015. The change in fair value of interest rate derivative instruments recognized in other comprehensive income was a loss of $1 million and a loss of $3 million for the three and six months ended June 30, 2016, respectively (2015 — nil and a loss of $1 million). For the three and six months ended June 30, 2016, the net realized loss related to the interest rate swaps was $1 million, and was included in financial charges and other (2015 — nil and $1 million). Refer to Note 14 — Financial Charges and Other.

The Partnership has no master netting agreements; however, it has derivative contracts containing provisions with rights of offset. The Partnership has elected to present the fair value of derivative instruments with the right to offset on a gross basis in the balance sheet. Had the Partnership elected to present these instruments on a net basis, there would be no effect on the consolidated balance sheet as of June 30, 2016 and December 31, 2015.

As discussed more fully in Note 16, we performed a discounted cash flow analysis to assess, for possible impairment, the $82 million of goodwill related to our acquisition of Tuscarora. The estimated fair value measurement is classified as Level 3. In the determination of the fair value, we used internal forecasts for expected future cash flows and applied appropriate discount rates. The determination of expected future cash flows involved significant assumptions and estimates regarding revenue, operating and maintenance costs and future growth capital.

ACCOUNTS RECEIVABLE AND OTHER

6 Months Ended

Jun. 30, 2016

ACCOUNTS RECEIVABLE AND OTHER

ACCOUNTS RECEIVABLE AND OTHER

NOTE 13ACCOUNTS RECEIVABLE AND OTHER

(unaudited)
(millions of dollars)	June 30, 2016	December 31, 2015

Trade accounts receivable, net of allowance of nil	30	31
Other	5	4

	35	35

FINANCIAL CHARGES AND OTHER

6 Months Ended

Jun. 30, 2016

FINANCIAL CHARGES AND OTHER

FINANCIAL CHARGES AND OTHER

NOTE 14FINANCIAL CHARGES AND OTHER

	Three months ended			Six months ended
(unaudited)	June 30,			June 30,
(millions of dollars)	2016		2015	2016		2015

Interest Expense (a)	16		16	33		29
Net realized loss related to the interest rate swaps	1		—	1		1
Other Income	(1	)	—	(1	)	(1	)

	16		16	33		29

(a)

Effective January 1, 2016, interest expense includes debt issuance costs and amortization of discount costs. Refer to Note 3, - Accounting Pronouncements.

CONTINGENCIES	6 Months Ended
CONTINGENCIES	Jun. 30, 2016
CONTINGENCIES
CONTINGENCIES	NOTE 15CONTINGENCIES Great Lakes v. Essar Steel Minnesota LLC, et al. — On October 29, 2009, Great Lakes filed suit in the U.S. District Court, District of Minnesota, against Essar Minnesota LLC and certain Essar affiliates (collectively, Essar) for breach of its monthly payment obligation under its transportation services agreement with Great Lakes. Great Lakes sought to recover approximately $33 million for past and future payments due under the agreement. On September 16, 2015, following a jury trial, the federal district court judge entered a judgment in the amount of $32.9 million in favor of Great Lakes. On September 20, 2015, Essar appealed the decision to the United States Court of Appeals for the 8th Circuit (8th Circuit) based on an allegation of improper jurisdiction and a number of other rulings by the federal district judge. Essar was required to post a performance bond for the full value of the judgment pending appeal. Both parties have filed their briefs. In July 2016, Essar filed for Bankruptcy and asked the 8th Circuit Court of Appeals to stay the appeal pending the bankruptcy proceeding. Great Lakes will file a request with the 8th Circuit Court of Appeals to deny the stay. Because Great Lakes has a performance bond for the full amount of the judgment, the bankruptcy proceeding is not expected to impact the ability of Great Lakes to receive payment of a final award. Employees Retirement System of the City of St. Louis v. TC PipeLines GP, Inc., et al. — On October 13, 2015, an alleged unitholder of the Partnership filed a class action and derivative complaint in the Delaware Court of Chancery (Chancery Court) against the General Partner, TransCanada American Investments, Ltd. (TAIL) and TransCanada, and the Partnership as a nominal defendant. The complaint alleges direct and derivative claims for breach of contract, breach of the duty of good faith and fair dealing, aiding and abetting breach of contract, and tortious interference in connection with the 2015 GTN Acquisition, including the issuance by the Partnership of $95 million in Class B Units and amendments to the Partnership Agreement to provide for the issuance of the Class B Units. Plaintiff seeks, among other things, to enjoin future issuances of Class B Units to TransCanada or any of its subsidiaries, disgorgement of certain distributions to the General Partner, TransCanada and any related entities, return of some or all of the Class B Units to the Partnership, rescission of the amendments to the Partnership Agreement, monetary damages and attorney fees. To the extent the claims are derivative, the Partnership would be the beneficiary of any monetary award. The Partnership does not expect legal fees or the impact of the decision on plaintiffs’ other requests to be material. In April 2016, the Chancery Court granted the Partnership and other defendants’ motion to dismiss the plaintiffs’ complaint. The plaintiff has appealed the decision to dismiss its claims. The appeal is expected to be heard in late-2016.

- Definition

The entire disclosure for loss and gain contingencies. Describes any existing condition, situation, or set of circumstances involving uncertainty as of the balance sheet date (or prior to issuance of the financial statements) as to a probable or reasonably possible loss incurred by an entity that will ultimately be resolved when one or more future events occur or fail to occur, and typically discloses the amount of loss recorded or a range of possible loss, or an assertion that no reasonable estimate can be made.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14472-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12021-110248

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14394-108349

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12053-110248

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14453-108349

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14615-108349

+ Details

GOODWILL AND REGULATORY	6 Months Ended
GOODWILL AND REGULATORY	Jun. 30, 2016
GOODWILL AND REGULATORY
GOODWILL AND REGULATORY	NOTE 16GOODWILL AND REGULATORY On January 21, 2016, the FERC issued an Order (the January 21 Order) initiating an investigation pursuant to Section 5 of the Natural Gas Act of 1938 (NGA) to determine whether Tuscarora’s existing rates for jurisdictional services are just and reasonable. On July 15, 2016, Tuscarora filed a petition with FERC requesting approval of the Stipulation and Agreement of Settlement (Tuscarora Settlement) that, if approved, will resolve the Section 5 rate review initiated by FERC in January 2016. Under the terms of the Tuscarora Settlement, Tuscarora’s system-wide unit rate will initially decrease by 16 percent, with an anticipated effective date of August 1, 2016. Unless superseded by a subsequent rate case or settlement, this rate will remain in effect for three years, after which time the unit rate will decrease an additional seven percent for an additional three years. The settlement does not contain a rate moratorium and requires Tuscarora to file to establish new rates no later than six years following the effective date of the initial settlement rates. We believe there is a high probability that the Tuscarora settlement will be approved as filed, and as a result, the expected reduction in Tuscarora’s future cash flows constituted a triggering event that led us to evaluate, for possible impairment, the $82 million of goodwill related to our acquisition of Tuscarora. Our analysis resulted in the estimated fair value of Tuscarora exceeding its carrying value but the excess was less than 10 percent. The fair value was measured using a discounted cash flow analysis and included revenue expected from Tuscarora’s current contracting level together with other opportunities on the system. There is a risk that reductions in future cash flow forecasts as a result of Tuscarora not being able to maintain its current contracting level and/or not being able to realize other opportunities on the system, together with adverse changes in other key assumptions such as projected operating costs and other future growth capital, could result in a future impairment of the goodwill balance relating to Tuscarora.

VARIABLE INTEREST ENTITIES

6 Months Ended

Jun. 30, 2016

VARIABLE INTEREST ENTITIES

VARIABLE INTEREST ENTITIES

NOTE 17 VARIABLE INTEREST ENTITIES

In the normal course of business, the Partnership must re-evaluate its legal entities under the newly effective consolidation guidance to determine if those that are considered to be VIEs are appropriately consolidated or if they should be accounted for under other GAAP. A variable interest entity (VIE) is a legal entity that does not have sufficient equity at risk to finance its activities without additional subordinated financial support or is structured such that equity investors lack the ability to make significant decisions relating to the entity’s operations through voting rights or do not substantively participate in the gains or losses of the entity. A VIE is appropriately consolidated if the Partnership is considered to be the primary beneficiary. The VIE’s primary beneficiary is the entity that has both (1) the power to direct the activities of the VIE that most significantly impact the VIEs economic performance and (2) the obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE.

As a result of its analysis, the Partnership continues to consolidate all legal entities in which it has a variable interest and for which it is considered to be the primary beneficiary. VIEs where the Partnership is not the primary beneficiary, but has a variable interest in the entity, are accounted for as equity investments.

Consolidated VIEs

The Partnership’s consolidated VIEs consist of the Partnership’s ILPs that hold interests in the Partnership’s pipeline systems. After considering the purpose and design of the ILPs and the risks that they were designed to create and pass through to the Partnership, the Partnership has concluded that it is the primary beneficiary of these ILPs because of the significant amount of variability that it absorbs from the ILPs’ economic performance.

The assets and liabilities held through these VIEs that are not available to creditors of the Partnership and whose investors have no recourse to the credit of the Partnership are held through GTN, Tuscarora, Northern Border, Great Lakes and PNGTS due to their third party debt. The following table presents the total assets and liabilities of these entities that are included in the Partnership’s Consolidated Balance Sheets:

(unaudited)
(millions of dollars)	June 30, 2016		December 31, 2015

ASSETS (LIABILITIES) *
Accounts receivable and other	21		25
Inventories	6		6
Equity investments	1,047		965
Plant, property and equipment	859		872
Other assets	2		2
Accounts payable and accrued liabilities	(18	)	(26	)
Accounts payable to affiliates, net	(18	)	(6	)
Accrued interest	(1	)	(1	)
Current portion of long-term debt	(15	)	(14	)
Long-term debt	(325	)	(326	)
Other liabilities	(25	)	(24	)

*North Baja and Bison, which are also assets held through our consolidated VIEs, are excluded as the assets of these entities can be used for purposes other than the settlement of the VIE’s obligations.

SUBSEQUENT EVENTS	6 Months Ended
SUBSEQUENT EVENTS	Jun. 30, 2016
SUBSEQUENT EVENTS
SUBSEQUENT EVENTS	NOTE 18SUBSEQUENT EVENTS Management of the Partnership has reviewed subsequent events through August 4, 2016, the date the financial statements were issued, and concluded there were no events or transactions during this period that would require recognition or disclosure in the consolidated financial statements other than what is disclosed here and/or those already disclosed in the preceding notes. On July 21, 2016, the board of directors of our General Partner declared the Partnership’s second quarter 2016 cash distribution in the amount of $0.94 per common unit payable on August 12, 2016 to unitholders of record as of August 1, 2016. The declared distribution reflects a $0.05 per common unit increase to the Partnership’s first quarter 2016 quarterly distribution and will include an IDR payment to our General Partner amounting to approximately $2 million. Northern Border declared its June 2016 distribution of $13 million on July 11, 2016, of which the Partnership will receive its 50 percent share or $6.5 million on July 29, 2016. Great Lakes declared its second quarter 2016 distribution of $12 million on July 19, 2016, of which the Partnership will receive its 46.45 percent share or $6 million on August 1, 2016.

SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
SIGNIFICANT ACCOUNTING POLICIES (Policies)	Jun. 30, 2016
SIGNIFICANT ACCOUNTING POLICIES
Use of Estimates	Use of Estimates The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Although management believes these estimates are reasonable, actual results could differ from these estimates.

EQUITY INVESTMENTS (Tables)

6 Months Ended

Jun. 30, 2016

EQUITY INVESTMENTS

Schedule of equity investments and summarized financial information for equity investees

	Ownership		Equity Earnings from Unconsolidated Affiliates				Investments in Unconsolidated Affiliates
	Interest at		Three months		Six Months
(unaudited)	June 30,		ended June 30,		ended June 30,		June 30,	December 31,
(millions of dollars)	2016		2016	2015	2016	2015	2016	2015

Northern Border (a)	50	%	16	15	34	34	455	480
Great Lakes	46.45	%	4	—	19	12	472	485
PNGTS (b)	49.90	%	2	—	11	—	120	—

			22	15	64	46	1,047	965

(a)

(b)

Northern Border

EQUITY INVESTMENTS

Schedule of equity investments and summarized financial information for equity investees

(unaudited)
(millions of dollars)	June 30, 2016		December 31, 2015

ASSETS
Cash and cash equivalents	16		27
Other current assets	34		33
Plant, property and equipment, net	1,108		1,124
Other assets (a)	15		16

	1,173		1,200


LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	40		39
Deferred credits and other	27		26
Long-term debt, including current maturities, net (a)	429		409
Partners’ equity
Partners’ capital	679		728
Accumulated other comprehensive loss	(2	)	(2	)

	1,173		1,200

(a)

	Three months ended				Six months ended
(unaudited)	June 30,				June 30,
(millions of dollars)	2016		2015		2016		2015

Transmission revenues	70		69		144		144
Operating expenses	(18	)	(18	)	(35	)	(34	)
Depreciation	(15	)	(14	)	(29	)	(29	)
Financial charges and other	(6	)	(6	)	(11	)	(11	)

Net income	31		31		69		70

Great Lakes

EQUITY INVESTMENTS

Schedule of equity investments and summarized financial information for equity investees

(unaudited)
(millions of dollars)	June 30, 2016	December 31, 2015

ASSETS
Current assets	53	86
Plant, property and equipment, net	721	727

	774	813


LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	29	31
Long-term debt, including current maturities, net (a)	288	297
Partners’ equity	457	485

	774	813

(a)

The application of ASU No. 2015-03 did not have a material effect on Great Lakes’ financial statements.

	Three months ended				Six months ended
(unaudited)	June 30,				June 30,
(millions of dollars)	2016		2015		2016		2015

Transmission revenues	36		28		97		76
Operating expenses	(15	)	(14	)	(30	)	(25	)
Depreciation	(7	)	(7	)	(14	)	(14	)
Financial charges and other	(5	)	(6	)	(11	)	(12	)

Net income	9		1		42		25

DEBT AND CREDIT FACILITIES (Tables)

6 Months Ended

Jun. 30, 2016

DEBT AND CREDIT FACILITIES

Schedule of debt and credit facilities

(unaudited) (millions of dollars)	June 30, 2016	December 31, 2015	Weighted Average Interest Rate for the Six Months Ended June 30, 2016

TC PipeLines, LP Senior Credit Facility due 2017	250	200	1.69	%
TC PipeLines, LP 2013 Term Loan Facility due 2018	500	500	1.69	%
TC PipeLines, LP 2015 Term Loan Facility due 2018	170	170	1.58	%
TC PipeLines, LP 4.65% Unsecured Senior Notes due 2021	350	350	4.65	%(b)
TC PipeLines, LP 4.375% Unsecured Senior Notes due 2025	350	350	4.375	%(b)
GTN 5.29% Unsecured Senior Notes due 2020	100	100	5.29	%(b)
GTN 5.69% Unsecured Senior Notes due 2035	150	150	5.69	%(b)
GTN Unsecured Term Loan Facility due 2019	65	75	1.38	%
Tuscarora Unsecured Term Loan due 2019	10	—	1.57	%
Tuscarora 3.82% Series D Senior Notes due 2017	16	16	3.82	%(b)

	1,961	1,911
Less: unamortized debt issuance costs and debt discount (a)	8	8
Less: current portion	15	14

	1,938	1,889

(a)

(b)

Fixed interest rate

Schedule of principal repayments required on debt

(unaudited)
(millions of dollars)

2016		4
2017		273
2018		691
2019		43
2020		100
Thereafter		850

		1,961

ACQUISITION (Tables)

6 Months Ended

Jun. 30, 2016

Portland Natural Gas Transmission System

EQUITY INVESTMENTS

Schedule of net purchase price of equity investment in PNGTS

(unaudited) (millions of dollars)
Net Purchase Price (a)		193
Less: TransCanada’s carrying value of PNGTS’ net assets at January 1, 2016		120

Excess purchase price (b)		73

(a)

Total purchase price of $228 million less the assumption of $35 million of proportional PNGTS debt by the Partnership.

(b)

The excess purchase price of $73 million was recorded as a reduction in Partners’ Equity.

NET INCOME PER COMMON UNIT (Tables)

6 Months Ended

Jun. 30, 2016

NET INCOME PER COMMON UNIT

Schedule of net income per common unit

	Three months ended						Six months ended
(unaudited)	June 30,						June 30,
(millions of dollars, except per common unit amounts)	2016			2015			2016			2015

Net income attributable to controlling interests	54			44			127			101
Net income attributable to the General Partner	(1		)	(1		)	(2		)	(2		)
Incentive distributions allocated to the General Partner (a)	(2		)	(1		)	(3		)	(1		)
Net income attributable to the Class B units (b)	(1		)	—			(1		)	—

Net income allocated to common units	50			42			121			98

Weighted average common units outstanding (millions) — basic and diluted	65.5		(c)	63.8			64.9		(c)	63.7
Net income per common unit — basic and diluted	$	0.76		$	0.66		$	1.86		$	1.53

(a)

(b)

(c)

Includes the common units subject to rescission. These units are treated as outstanding for financial reporting purposes (Refer to Note 7).

CHANGE IN OPERATING WORKING CAPITAL (Tables)

6 Months Ended

Jun. 30, 2016

CHANGE IN OPERATING WORKING CAPITAL

Schedule of change in operating working capital

(unaudited)	Six months ended June 30,
(millions of dollars)	2016	2015

Change in accounts receivable and other	—	4
Change in accounts payable and accrued liabilities (a)	2	(2	)
Change in accounts payable to affiliates	—	(5	)
Change in accrued interest	1	4

Change in operating working capital	3	1

(a)

RELATED PARTY TRANSACTIONS (Tables)

6 Months Ended

Jun. 30, 2016

RELATED PARTY TRANSACTIONS

Summary of capital and operating costs charged to pipeline systems by related party

	Three months ended		Six months ended
(unaudited)	June 30,		June 30,
(millions of dollars)	2016	2015	2016	2015

Capital and operating costs charged by TransCanada’s subsidiaries to:
Great Lakes (a)	7	8	14	14
Northern Border (a)	9	9	15	16
PNGTS (a), (c)	2	—	4	—
GTN (a), (b)	7	8	13	14
Bison (d)	1	1	—	2
North Baja	1	2	2	3
Tuscarora	1	1	2	2
Impact on the Partnership’s net income:
Great Lakes	3	3	6	6
Northern Border	3	4	6	7
PNGTS (c)	1	—	2	—
GTN (b)	6	7	11	11
Bison	1	1	2	2
North Baja	1	1	2	2
Tuscarora	1	1	2	2

Summary of amount payable to related party for costs charged

(unaudited)
(millions of dollars)	June 30, 2016	December 31, 2015

Net amounts payable to TransCanada’s subsidiaries is as follows:
Great Lakes (a)	3	3
Northern Border (a)	3	5
PNGTS (a)	1	—
GTN	3	3
Bison	1	—
North Baja	—	—
Tuscarora	1	1

(a)

Represents 100 percent of the costs.

(b)

In April 2015, the Partnership acquired the remaining 30 percent interest in GTN.

(c)

In January 2016, the Partnership acquired 49.9 percent interest in PNGTS.

(d)

Net of proceeds of $1 million from the sale of excess pipe (at cost) to an affiliate.

ACCOUNTS RECEIVABLE AND OTHER (Tables)

6 Months Ended

Jun. 30, 2016

ACCOUNTS RECEIVABLE AND OTHER

Schedule of accounts receivable and other

(unaudited)
(millions of dollars)	June 30, 2016	December 31, 2015

Trade accounts receivable, net of allowance of nil	30	31
Other	5	4

	35	35

FINANCIAL CHARGES AND OTHER (Tables)

6 Months Ended

Jun. 30, 2016

FINANCIAL CHARGES AND OTHER

Schedule of components of financial charges and other

	Three months ended			Six months ended
(unaudited)	June 30,			June 30,
(millions of dollars)	2016		2015	2016		2015

Interest Expense (a)	16		16	33		29
Net realized loss related to the interest rate swaps	1		—	1		1
Other Income	(1	)	—	(1	)	(1	)

	16		16	33		29

(a)

Effective January 1, 2016, interest expense includes debt issuance costs and amortization of discount costs. Refer to Note 3, - Accounting Pronouncements.

VARIABLE INTEREST ENTITIES (Tables)

6 Months Ended

Jun. 30, 2016

VARIABLE INTEREST ENTITIES

Schedule of assets and liabilities held through VIEs whose assets cannot be used for purposes other settlement of their obligations

(unaudited)
(millions of dollars)	June 30, 2016		December 31, 2015

ASSETS (LIABILITIES) *
Accounts receivable and other	21		25
Inventories	6		6
Equity investments	1,047		965
Plant, property and equipment	859		872
Other assets	2		2
Accounts payable and accrued liabilities	(18	)	(26	)
Accounts payable to affiliates, net	(18	)	(6	)
Accrued interest	(1	)	(1	)
Current portion of long-term debt	(15	)	(14	)
Long-term debt	(325	)	(326	)
Other liabilities	(25	)	(24	)

- Definition

Tabular disclosure of the significant judgments and assumptions made in determining whether a variable interest (as defined) held by the entity requires the variable interest entity (VIE) (as defined) to be consolidated and (or) disclose information about its involvement with the VIE, individually or in aggregate (as applicable); the nature of restrictions, if any, on the consolidated VIE's assets and on the settlement of its liabilities reported by an entity in its statement of financial position, including the carrying amounts of such assets and liabilities; the nature of, and changes in, the risks associated with involvement in the VIE; how involvement with the VIE affects the entity's financial position, financial performance, and cash flows; the lack of recourse if creditors (or beneficial interest holders) of the consolidated VIE have no recourse to the general credit of the primary beneficiary (if applicable); the terms of arrangements, giving consideration to both explicit arrangements and implicit variable interests, if any, that could require the entity to provide financial support to the VIE, including events or circumstances that could expose the entity to a loss; the methodology used by the entity for determining whether or not it is the primary beneficiary of the variable interest entity; the significant factors considered and judgments made in determining that the power to direct the activities of a VIE that most significantly impact the VIE's economic performance are shared (as defined); the carrying amounts and classification of assets and liabilities of the VIE included in the statement of financial position; the entity's maximum exposure to loss, if any, as a result of its involvement with the VIE, including how the maximum exposure is determined and significant sources of the entity's exposure to the VIE; a comparison of the carrying amounts of the assets and liabilities and the entity's maximum exposure to loss; information about any liquidity arrangements, guarantees, and (or) other commitments by third parties that may affect the fair value or risk of the entity's variable interest in the VIE; whether or not the entity has provided financial support or other support (explicitly or implicitly) to the VIE that it was not previously contractually required to provide or whether the entity intends to provide that support, including the type and amount of the support and the primary reasons for providing the support; and supplemental information the entity determines necessary to provide.

+ References + Details

ORGANIZATION - Ownership Interests in Natural Gas Pipeline Systems (Details)	6 Months Ended
	Jun. 30, 2016 LimitedPartnership
ORGANIZATION
Number of intermediate limited partnerships through which pipeline assets are owned	3

ACCOUNTING PRONOUNCEMENTS - Imputation of Interest (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
ACCOUNTING PRONOUNCEMENTS
Other assets		$ 1
Long-term debt	$ 1,938	1,889
ASU 2015-03, Interest - Imputation of Interest \| Adjustment
ACCOUNTING PRONOUNCEMENTS
Other assets		(7)
Long-term debt		$ (7)

EQUITY INVESTMENTS (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended
EQUITY INVESTMENTS (Details) - USD ($) $ in Millions	Apr. 30, 2006	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jul. 18, 2016	Jan. 01, 2016	Dec. 31, 2015
EQUITY INVESTMENTS
Equity Earnings		$ 22		$ 15	$ 64	$ 46
Equity Investments		$ 1,047			$ 1,047				$ 965
Great Lakes
EQUITY INVESTMENTS
Total cash call issued to fund debt repayment			$ 9
Northern Border
EQUITY INVESTMENTS
Ownership interest (as a percent)		50.00%			50.00%
Equity Earnings		$ 16		15	$ 34	34
Equity Investments		455			455				480
Amortization period of transaction fee	12 years
Transaction fee	$ 10
Additional ownership interest acquired (as a percent)	20.00%
Assets
Cash and cash equivalents		16			16				27
Other current assets		34			34				33
Plant, property and equipment, net		1,108			1,108				1,124
Other assets		15			15				16
Assets, total		1,173			1,173				1,200
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		40			40				39
Deferred credits and other		27			27				26
Long-term debt, including current maturities, net		429			429				409
Partners' equity
Partners' equity		679			679				728
Accumulated other comprehensive loss		(2)			(2)				(2)
Liabilities and Partners' Equity, total		1,173			1,173				1,200
Revenues (expenses)
Transmission revenues		70		69	144	144
Operating expenses		(18)		(18)	(35)	(34)
Depreciation		(15)		(14)	(29)	(29)
Financial charges and other		(6)		(6)	(11)	(11)
Net income		$ 31		31	$ 69	70
Great Lakes
EQUITY INVESTMENTS
Ownership interest (as a percent)		46.45%	46.45%		46.45%
Equity Earnings		$ 4			$ 19	12
Equity Investments		472			472				485
Equity contribution			$ 4		4	4
Assets
Current assets		53			53				86
Plant, property and equipment, net		721			721				727
Assets, total		774			774				813
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		29			29				31
Long-term debt, including current maturities, net		288			288				297
Partners' equity
Partners' equity		457			457				485
Liabilities and Partners' Equity, total		774			774				813
Revenues (expenses)
Transmission revenues		36		28	97	76
Operating expenses		(15)		(14)	(30)	(25)
Depreciation		(7)		(7)	(14)	(14)
Financial charges and other		(5)		(6)	(11)	(12)
Net income		$ 9		$ 1	$ 42	$ 25
Portland Natural Gas Transmission System
EQUITY INVESTMENTS
Ownership interest (as a percent)		49.90%			49.90%		49.90%	49.90%
Equity Earnings		$ 2			$ 11
Equity Investments		120			120
Undistributed earnings		$ 0			0
Equity contribution					$ 193
ASU 2015-03, Interest - Imputation of Interest \| Adjustment \| Northern Border
Assets
Other assets									(2)
LIABILITIES AND PARTNERS' EQUITY
Long-term debt, including current maturities, net									$ (2)

DEBT AND CREDIT FACILITIES - Amounts Outstanding and Description of Terms (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015	Jun. 30, 2016 USD ($) entity	Jun. 30, 2015 USD ($)	Apr. 29, 2016 USD ($)	Dec. 31, 2015 USD ($)
Credit facilities, short-term loan facility and long-term debt
Other assets						$ 1,000,000
Debt and credit facilities	$ 1,961,000,000		$ 1,961,000,000			1,911,000,000
Less: unamortized debt issuance costs and debt discount	8,000,000		8,000,000			8,000,000
Less: current portion	15,000,000		15,000,000			14,000,000
Long-term debt	$ 1,938,000,000		1,938,000,000			1,889,000,000
Amount borrowed			$ 205,000,000	$ 424,000,000
Senior Credit Facility and the Term Loan Facilities due in 2018
Credit facilities, short-term loan facility and long-term debt
Leverage ratio, actual (as a percent)	437.00%		437.00%
Senior Credit Facility and the Term Loan Facilities due in 2018 \| Debt agreement covenants, initial period after occurrence of acquisition
Credit facilities, short-term loan facility and long-term debt
Additional period immediately following the fiscal quarter in which a specified material acquisition occurs			6 months
Senior Credit Facility and the Term Loan Facilities due in 2018 \| Debt agreement covenants, initial period after occurrence of acquisition \| Minimum
Credit facilities, short-term loan facility and long-term debt
Number of acquisitions \| entity			1
Senior Credit Facility and the Term Loan Facilities due in 2018 \| Debt agreement covenants, initial period after occurrence of acquisition \| Maximum
Credit facilities, short-term loan facility and long-term debt
Leverage ratio, covenant (as a percent)			550.00%
Senior Credit Facility and the Term Loan Facilities due in 2018 \| Debt agreement covenants, periods subsequent to initial period after occurrence of acquisition \| Maximum
Credit facilities, short-term loan facility and long-term debt
Leverage ratio, covenant (as a percent)			500.00%
Revolving credit facility \| TC PipeLines, LP Senior Credit Facility due 2017
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	$ 250,000,000		$ 250,000,000			200,000,000
Weighted Average Interest Rate (as a percent)			1.69%
Maximum borrowing capacity	500,000,000		$ 500,000,000
Amount outstanding under credit facility	250,000,000		250,000,000			200,000,000
Remaining borrowing capacity	250,000,000		250,000,000
Term loan \| TC PipeLines, LP 2013 Term Loan Facility due 2018
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	$ 500,000,000		$ 500,000,000			$ 500,000,000
Weighted Average Interest Rate (as a percent)			1.69%
Term loan \| TC PipeLines, LP 2013 Term Loan Facility due 2018 \| LIBOR borrowings \| LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end (as a percent)	1.71%		1.71%			1.50%
Term loan \| TC PipeLines, LP 2013 Term Loan Facility due 2018 \| LIBOR borrowings \| LIBOR \| Hedges of cash flows \| Interest rate swaps
Credit facilities, short-term loan facility and long-term debt
Weighted Average Interest Rate (as a percent)	2.31%	1.84%	2.25%	1.84%
Term loan \| TC PipeLines, LP 2015 Term Loan Facility due 2018
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	$ 170,000,000		$ 170,000,000			$ 170,000,000
Weighted Average Interest Rate (as a percent)			1.58%
Unsecured debt \| TC PipeLines, LP 4.65% Senior Notes due 2021
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	4.65%		4.65%			4.65%
Debt and credit facilities	$ 350,000,000		$ 350,000,000			$ 350,000,000
Weighted Average Interest Rate (as a percent)			4.65%
Unsecured debt \| TC PipeLines, LP 4.375% Senior Notes due 2025
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	4.375%		4.375%			4.375%
Debt and credit facilities	$ 350,000,000		$ 350,000,000			$ 350,000,000
Weighted Average Interest Rate (as a percent)			4.375%
Unsecured debt \| GTN 5.29% Senior Notes due 2020
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	5.29%		5.29%			5.29%
Debt and credit facilities	$ 100,000,000		$ 100,000,000			$ 100,000,000
Weighted Average Interest Rate (as a percent)			5.29%
Unsecured debt \| GTN 5.69% Senior Notes due 2035
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	5.69%		5.69%			5.69%
Debt and credit facilities	$ 150,000,000		$ 150,000,000			$ 150,000,000
Weighted Average Interest Rate (as a percent)			5.69%
Unsecured debt \| GTN Term Loan Facility due 2019
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	65,000,000		$ 65,000,000			$ 75,000,000
Weighted Average Interest Rate (as a percent)			1.38%
Unsecured debt \| Tuscarora Term Loan due 2019
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	$ 10,000,000		$ 10,000,000
Weighted Average Interest Rate (as a percent)			1.57%
Secured debt \| Tuscarora 3.82% Series D Senior Notes due 2017
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	3.82%		3.82%			3.82%
Debt and credit facilities	$ 16,000,000		$ 16,000,000			$ 16,000,000
Weighted Average Interest Rate (as a percent)			3.82%
GTN \| Unsecured debt \| Senior Notes and Term Loan Facility due 2019
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization, actual	43.70%		43.70%
GTN \| Unsecured debt \| Senior Notes and Term Loan Facility due 2019 \| Maximum
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization, covenant			70.00%
Tuscarora Gas Transmission Company \| Unsecured debt \| Tuscarora Term Loan due 2019
Credit facilities, short-term loan facility and long-term debt
Amount of debt					$ 9,500,000
Tuscarora Gas Transmission Company \| Unsecured debt \| Tuscarora Term Loan due 2019 \| LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end (as a percent)	1.59%		1.59%
Tuscarora Gas Transmission Company \| Unsecured debt \| Tuscarora 3.82% Series D Senior Notes due 2017
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization, actual	24.00%		24.00%
Debt Service Coverage, Actual (as a percent)			457.00%
Tuscarora Gas Transmission Company \| Unsecured debt \| Tuscarora 3.82% Series D Senior Notes due 2017 \| Minimum
Credit facilities, short-term loan facility and long-term debt
Debt Service Coverage, covenant (as a percent)			300.00%
Tuscarora Gas Transmission Company \| Unsecured debt \| Tuscarora 3.82% Series D Senior Notes due 2017 \| Maximum
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization, covenant			45.00%
ASU 2015-03, Interest - Imputation of Interest \| Adjustment
Credit facilities, short-term loan facility and long-term debt
Other assets						(7,000,000)
Long-term debt						$ (7,000,000)

DEBT AND CREDIT FACILITIES - Principal Payments Required (Details) $ in Millions	Jun. 30, 2016 USD ($)
Principal repayments required on debt
2016	$ 4
2017	273
2018	691
2019	43
2020	100
Thereafter	850
Total debt	$ 1,961

ACQUISITION - Acquisition of Ownership Interest in PNGTS (Details) - Portland Natural Gas Transmission System - USD ($) $ in Millions		6 Months Ended
	Jan. 01, 2016	Jun. 30, 2016	Jul. 18, 2016
Acquisition
Interest acquired (as a percent)	49.90%	49.90%	49.90%
Net purchase price		$ 193
TransCanada \| Transaction between entities under common control
Acquisition
Total purchase price	$ 228
Net purchase price	193
Purchase price adjustments	5
Assumption of proportional debt	35
Additional contingent payment, minimum	5
Additional contingent payment, maximum	$ 50
Period following closing date during which additional payments may be required	15 years

ACQUISITION - Net Purchase Price of PNGTS (Details) - USD ($) $ in Millions		6 Months Ended
	Jan. 01, 2016	Jun. 30, 2016
EQUITY INVESTMENTS
Reduction in Partners' Equity		$ 73
Portland Natural Gas Transmission System
EQUITY INVESTMENTS
Net purchase price		$ 193
Transaction between entities under common control \| TransCanada \| Portland Natural Gas Transmission System
EQUITY INVESTMENTS
Net purchase price	$ 193
Less: TransCanada's carrying value of PNGTS' net assets	(120)
Excess purchase price	73
Total purchase price	228
Proportional debt	35
Common units and General Partner interest combined \| Transaction between entities under common control \| TransCanada \| Portland Natural Gas Transmission System
EQUITY INVESTMENTS
Reduction in Partners' Equity	$ 73

PARTNERS' EQUITY - ATM Equity Issuance Program (Details) - USD ($)		3 Months Ended		4 Months Ended		6 Months Ended
	Jul. 29, 2016	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2016	Jun. 30, 2016	Jun. 30, 2015
Partners' Equity
Net proceeds from public offering of common units						$ 83,000,000
Common units issuance subject to rescission net						83,000,000
General Partner
Partners' Equity
Net proceeds from public offering of common units						2,000,000
Common units issuance subject to rescission net						$ 2,000,000
TC PipeLines GP, Inc. \| General Partner
Partners' Equity
Ownership interest in the Partnership (as a percent)		2.00%	2.00%			2.00%	2.00%
ATM Equity Issuance Program \| Common units
Partners' Equity
Units sold						1,619,631
Net proceeds from public offering of common units						$ 81,000,000
Sales agent commissions						823,000
Amended shelf registation with SEC	$ 400,000,000
Common units issuance subject to rescission net					$ 82,334,015
ATM Equity Issuance Program \| TC PipeLines GP, Inc. \| General Partner
Partners' Equity
Equity contribution						$ 2,000,000
ATM Equity Issuance Program \| Minimum \| Common units
Partners' Equity
Common units (price per unit)					$ 47.00
ATM Equity Issuance Program \| Maximum \| Common units
Partners' Equity
Common units (price per unit)					$ 54.95
Period of time for Section 5 Securities violations to be filed within				1 year

PARTNERS' EQUITY - Class B Units (Details) - USD ($)	3 Months Ended		6 Months Ended
PARTNERS' EQUITY - Class B Units (Details) - USD ($)	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2016	Jun. 30, 2015
Class B units
Partners' Equity
Net income allocated to limited partners	$ 1,000,000		$ 1,000,000
Distribution declared		$ 12,000,000
Distribution paid		$ 12,000,000	12,000,000
GTN
Partners' Equity
30% of GTN's distributable cash flow			$ 21,000,000
GTN \| TransCanada \| Distributions \| Class B units
Partners' Equity
Portion of GTN's annual distributions to which the Class B units are entitled to receive a percentage share of the distributions above threshold (as a percent)			30.00%
Percentage applied to 30 percent of GTN's distributions above threshold through March 31, 2020			100.00%
Threshold of GTN's total distributable cash flows for payment to Class B units			$ 20,000,000
Percentage applied to GTN's distributions above threshold after March 31, 2020			25.00%
Percentage applied to GTN's distributable cash flow for the twelve month period ending December 31, 2016			30.00%
30% of GTN's distributable cash flow			$ 21,000,000	$ 0

NET INCOME PER COMMON UNIT - General Partner Effective Interest and Allocated Incentive Distributions (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Partners' Equity
Incentive distributions allocated to the General Partner	$ 2	$ 1	$ 3	$ 1
TC PipeLines GP, Inc. \| General Partner
Partners' Equity
General partner interest (as a percent)	2.00%	2.00%	2.00%	2.00%

NET INCOME PER COMMON UNIT - Terms of Class B Unit Distributions and Determination of Net Income per Common Unit (Details) - USD ($) $ / shares in Units, shares in Millions	3 Months Ended		6 Months Ended		9 Months Ended	12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2016
Net income (loss) per common unit
Net income attributable to controlling interests	$ 54,000,000	$ 44,000,000	$ 127,000,000	$ 101,000,000
Net income attributable to the General Partner	(1,000,000)	(1,000,000)	(2,000,000)	(2,000,000)
Incentive distributions attributable to the General Partner	(2,000,000)	(1,000,000)	(3,000,000)	(1,000,000)
Class B units
Net income (loss) per common unit
Net income allocated to limited partners	1,000,000		1,000,000
Common units
Net income (loss) per common unit
Net income allocated to limited partners	$ 50,000,000	$ 42,000,000	$ 121,000,000	$ 98,000,000
Weighted average common units outstanding - basic (in units)	65.5	63.8	64.9	63.7
Weighted average common units outstanding - diluted (in units)	65.5	63.8	64.9	63.7
Net income per common unit - basic (in dollars per unit)	$ 0.76	$ 0.66	$ 1.86	$ 1.53
Net income per common unit - diluted (in dollars per unit)	$ 0.76	$ 0.66	$ 1.86	$ 1.53
GTN
Distributions
30% of GTN's distributable cash flow			$ 21,000,000
GTN \| Class B units \| TransCanada \| Distributions
Distributions
Percentage applied to GTN's distributable cash flow for the twelve month period ending December 31, 2016			30.00%
Threshold of GTN's total distributable cash flows for payment to Class B units			$ 20,000,000
Prorated threshold of GTN's distributions for payment to Class B units					$ 15,000,000	$ 20,000,000
30% of GTN's distributable cash flow			$ 21,000,000	$ 0

CASH DISTRIBUTIONS - Distributions Paid (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Distributions
Incentive distribution paid to the General Partner	$ 1.0	$ 0.3	$ 2.0	$ 0.6
Common units
Distributions
Per Unit Distribution, paid (in dollars per unit)	$ 0.89	$ 0.84	$ 1.78	$ 1.68
Common units and General Partner interest combined
Distributions
Total cash distribution	$ 60.0	$ 55.0	$ 119.0	$ 110.0
TC PipeLines GP, Inc. \| General Partner
Distributions
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest	2.00%	2.00%	2.00%	2.00%

CHANGE IN OPERATING WORKING CAPITAL - Components (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
CHANGE IN OPERATING WORKING CAPITAL
Change in accounts receivable and other		$ 4
Change in accounts payable and accrued liabilities	$ 2	(2)
Change in accounts payable to affiliates		(5)
Change in accrued interest	1	4
Change in operating working capital	$ 3	$ 1

CHANGE IN OPERATING WORKING CAPITAL - GTN's Carty Lateral Construction Accrual (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended		12 Months Ended
	Mar. 31, 2016	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Non-cash items
Capital expenditures		$ 18	$ 12
GTN
Non-cash items
Accruals for capital expenditures				$ 10
Capital expenditures	$ 10

RELATED PARTY TRANSACTIONS (Details) - USD ($) $ in Millions			3 Months Ended			4 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	May 03, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2014	Jul. 18, 2016	Mar. 31, 2016	Jan. 01, 2016	Apr. 01, 2015
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	$ 5.0	$ 5.0	$ 5.0	$ 5.0			$ 5.0
Great Lakes
Capital and operating costs charged to the pipeline systems and amount payable
Interest acquired (as a percent)	46.45%		46.45%				46.45%				46.45%
Northern Border
Capital and operating costs charged to the pipeline systems and amount payable
Interest acquired (as a percent)	50.00%		50.00%				50.00%
Portland Natural Gas Transmission System
Capital and operating costs charged to the pipeline systems and amount payable
Interest acquired (as a percent)	49.90%		49.90%				49.90%			49.90%		49.90%
General Partner \| Reimbursement of costs of services provided
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			$ 1.0		$ 1.0		$ 2.0	$ 1.0
TransCanada's subsidiaries \| Great Lakes
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	$ 3.0	3.0	3.0	3.0			3.0
Net amounts (receivable)	$ (9.0)	$ (17.0)	(9.0)	(17.0)			(9.0)
Percentage of capital and operating costs charged	100.00%	100.00%
Amount included in receivables from related party	$ 9.0	$ 17.0	9.0	17.0			9.0
TransCanada's subsidiaries \| Great Lakes \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			$ 7.0		$ 8.0		$ 14.0	$ 14.0
Percentage of capital and operating costs charged			100.00%		100.00%		100.00%	100.00%
TransCanada's subsidiaries \| Great Lakes \| Transportation contracts
Capital and operating costs charged to the pipeline systems and amount payable
Revenues from related party			$ 23.0		$ 18.0		$ 69.0	$ 47.0
TransCanada's subsidiaries \| Great Lakes \| Transportation contracts \| Total revenues \| Customer concentration risk
Capital and operating costs charged to the pipeline systems and amount payable
Percent of total revenues			64.00%		63.00%		71.00%	62.00%
TransCanada's subsidiaries \| Great Lakes \| Affiliated rental revenue
Capital and operating costs charged to the pipeline systems and amount payable
Revenues from related party			$ 1.0		$ 1.0		$ 1.0	$ 1.0
TransCanada's subsidiaries \| Northern Border
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	$ 3.0	$ 5.0	3.0	5.0			3.0
Percentage of capital and operating costs charged	100.00%	100.00%
TransCanada's subsidiaries \| Northern Border \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			$ 9.0		$ 9.0		$ 15.0	$ 16.0
Percentage of capital and operating costs charged			100.00%		100.00%		100.00%	100.00%
TransCanada's subsidiaries \| Portland Natural Gas Transmission System
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	$ 1.0		$ 1.0				$ 1.0
Percentage of capital and operating costs charged	100.00%
TransCanada's subsidiaries \| Portland Natural Gas Transmission System \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			$ 2.0				$ 4.0
Percentage of capital and operating costs charged			100.00%				100.00%
TransCanada's subsidiaries \| GTN
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	$ 3.0	$ 3.0	$ 3.0	3.0			$ 3.0
TransCanada's subsidiaries \| GTN \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			7.0		$ 8.0		13.0	$ 14.0
Impact on the Partnership's net income attributable to controlling interests			$ 6.0		$ 7.0		$ 11.0	$ 11.0
Percentage of capital and operating costs charged			100.00%		100.00%		100.00%	100.00%
TransCanada's subsidiaries \| Bison
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	1.0		$ 1.0				$ 1.0
TransCanada's subsidiaries \| Bison \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			1.0		$ 1.0			$ 2.0
Impact on the Partnership's net income attributable to controlling interests			1.0		1.0		2.0	2.0
Net proceeds from the sale of excess pipe to an affiliate							1.0
TransCanada's subsidiaries \| North Baja Pipeline, LLC \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			1.0		2.0		2.0	3.0
Impact on the Partnership's net income attributable to controlling interests			1.0		1.0		2.0	2.0
TransCanada's subsidiaries \| Tuscarora Gas Transmission Company
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	$ 1.0	$ 1.0	1.0	1.0			1.0
TransCanada's subsidiaries \| Tuscarora Gas Transmission Company \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			1.0		1.0		2.0	2.0
Impact on the Partnership's net income attributable to controlling interests			1.0		1.0		2.0	2.0
TransCanada's subsidiaries \| Great Lakes
Capital and operating costs charged to the pipeline systems and amount payable
Revenue from TransCanada and its affiliates included in the Partnership's equity earnings			10.0		8.0		32.0	22.0
TransCanada's subsidiaries \| Great Lakes \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Impact on the Partnership's net income attributable to controlling interests			3.0		3.0		6.0	6.0
TransCanada's subsidiaries \| Northern Border \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Impact on the Partnership's net income attributable to controlling interests			3.0		$ 4.0		6.0	$ 7.0
TransCanada's subsidiaries \| Portland Natural Gas Transmission System \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Impact on the Partnership's net income attributable to controlling interests			$ 1.0				$ 2.0
Former parent, TransCanada subsidiaries \| Transaction between entities under common control \| GTN
Capital and operating costs charged to the pipeline systems and amount payable
Interest acquired (as a percent)	30.00%		30.00%				30.00%						30.00%
ANR Pipeline Company \| Great Lakes \| Firm service between Michigan and Wisconsin
Capital and operating costs charged to the pipeline systems and amount payable
Deferred revenue related to services performed						$ 14.0			$ 9.0
Deferred revenue recognized				$ 23.0

RELATED PARTY TRANSACTIONS - Distribution from Affiliate (Details) - USD ($) $ in Millions			6 Months Ended
	Jul. 18, 2016	Jun. 16, 2016	Jun. 30, 2016	Jan. 01, 2016
Related party transactions
Partnership distribution			$ 131
Portland Natural Gas Transmission System
Related party transactions
Ownership interest (as a percent)	49.90%		49.90%	49.90%
Distribution declared \| Portland Natural Gas Transmission System
Related party transactions
Partnership distribution		$ 8
Cash Distribution Paid \| Portland Natural Gas Transmission System
Related party transactions
Partnership's share of distributions declared and payable by investee	$ 4

FAIR VALUE MEASUREMENTS - Estimated Fair Value of Debt (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Fair Value \| Level 2
Financial Instruments
Fair value of debt	$ 1,994	$ 1,873

FAIR VALUE MEASUREMENTS - Interest Rate Swaps (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Interest rate derivatives
Goodwill	$ 130		$ 130		$ 130
Tuscarora Gas Transmission Company
Interest rate derivatives
Goodwill	$ 82		$ 82
Interest rate swaps \| Term loan \| TC PipeLines, LP 2013 Term Loan Facility due 2018
Interest rate derivatives
Weighted average fixed interest rate (as a percent)	2.31%		2.31%
Hedges of cash flows \| Interest rate swaps
Interest rate derivatives
Change in fair value of interest rate derivative instruments recognized in other comprehensive income	$ 1	$ 0	$ 3	$ 1
Hedges of cash flows \| Interest rate swaps \| Financial charges and other.
Interest rate derivatives
Net realized loss related to the interest rate swaps	1	$ 0	1	$ 1
Designated as hedge \| Interest rate swaps \| Recurring fair value measurement \| Level 2
Interest rate derivatives
Fair value of derivatives, gross	5		5		1
Fair value of derivatives, net	$ 5		$ 5		$ 1

ACCOUNTS RECEIVABLE AND OTHER (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
ACCOUNTS RECEIVABLE AND OTHER
Trade accounts receivable, net of allowance of nil	$ 30	$ 31
Other	5	4
Accounts receivable and other	35	35
Trade accounts receivable, allowance	$ 0	$ 0

FINANCIAL CHARGES AND OTHER (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
FINANCIAL CHARGES AND OTHER
Interest Expense	$ 16	$ 16	$ 33	$ 29
Net realized loss related to the interest rate swaps	1		1	1
Other Income	(1)		(1)	(1)
Financial charges and other	$ 16	$ 16	$ 33	$ 29

CONTINGENCIES (Details) - USD ($) $ in Millions	Sep. 16, 2015	Apr. 01, 2015	Oct. 29, 2009
Former parent, TransCanada subsidiaries \| Transaction between entities under common control \| GTN \| Partnership interest \| Class B units
Contingencies
Equity issuance		$ 95.0
Great Lakes v. Essar Steel Minnesota LLC, et al. \| Great Lakes \| Essar
Contingencies
Recovery sought			$ 33.0
Judgement awarded	$ 32.9

GOODWILL AND REGULATORY (Details) - USD ($) $ in Millions	Aug. 01, 2016	Jun. 30, 2016	Dec. 31, 2015
Goodwill and Regulatory Matters
Goodwill		$ 130	$ 130
Tuscarora Gas Transmission Company
Goodwill and Regulatory Matters
Goodwill		82
Tuscarora Gas Transmission Company \| Tuscarora Settlement \| FERC
Goodwill and Regulatory Matters
Decrease of system-wide unit rate (as a percent)	16.00%
Terms of the settlement	Unless superseded by a subsequent rate case or settlement, this rate will remain in effect for three years, after which time the unit rate will decrease an additional seven percent for an additional three years.
Goodwill		$ 82
Tuscarora Gas Transmission Company \| Tuscarora Settlement \| FERC \| Maximum
Goodwill and Regulatory Matters
Estimated Fair value over carrying value (as a percent)		10.00%
Tuscarora Gas Transmission Company \| Tuscarora Settlement \| FERC \| Minimum
Goodwill and Regulatory Matters
Term to establish new rates	6 years

VARIABLE INTEREST ENTITIES - Consolidated VIEs (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
ASSETS (LIABILITIES)
Accounts receivable and other	$ 35	$ 35
Inventories	7	7
Equity investments	1,047	965
Plant, property and equipment	1,913	1,949
Other assets		1
Accounts payable and accrued liabilities	(26)	(32)
Accounts payable to affiliates	(5)	(5)
Accrued interest	(9)	(8)
Current portion of long-term debt	(15)	(14)
Long-term debt	(1,938)	(1,889)
Other liabilities	(29)	(27)
Consolidated VIEs \| Restricted VIEs
ASSETS (LIABILITIES)
Accounts receivable and other	21	25
Inventories	6	6
Equity investments	1,047	965
Plant, property and equipment	859	872
Other assets	2	2
Accounts payable and accrued liabilities	(18)	(26)
Accounts payable to affiliates	(18)	(6)
Accrued interest	(1)	(1)
Current portion of long-term debt	(15)	(14)
Long-term debt	(325)	(326)
Other liabilities	$ (25)	$ (24)

SUBSEQUENT EVENTS - Quarter Distribution per Common Unit (Details)	Jul. 21, 2016 $ / shares
Subsequent event \| Common units
Distributions
Distribution (in dollars per unit)	$ 0.94

SUBSEQUENT EVENTS - Unconsolidated Affiliate Distributions (Details) - USD ($) $ / shares in Units, $ in Millions						3 Months Ended		6 Months Ended
	Aug. 01, 2016	Jul. 29, 2016	Jul. 21, 2016	Jul. 19, 2016	Jul. 11, 2016	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Mar. 31, 2016
Subsequent events
Partnership distribution								$ 131.0
Distribution Made to General Partner, Incentive Cash Distributions Paid						$ 1.0	$ 0.3	2.0	$ 0.6
General Partner IDRs paid						$ 1.0	$ 0.3	$ 2.0	$ 0.6
Northern Border
Subsequent events
Ownership interest (as a percent)						50.00%		50.00%
Great Lakes
Subsequent events
Ownership interest (as a percent)						46.45%		46.45%		46.45%
Subsequent event \| Distribution declared
Subsequent events
Distribution Made to General Partner, Incentive Cash Distributions Paid			$ 2.0
General Partner IDRs paid			$ 2.0
Increase to Partnership's quarterly distribution (per unit)			$ 0.05
Subsequent event \| Distribution declared \| Northern Border
Subsequent events
Partnership distribution					$ 13.0
Subsequent event \| Distribution declared \| Great Lakes
Subsequent events
Partnership distribution				$ 12.0
Subsequent event \| Cash Distribution Paid \| Northern Border
Subsequent events
Partnership's share of distributions		$ 6.5
Subsequent event \| Cash Distribution Paid \| Great Lakes
Subsequent events
Partnership's share of distributions	$ 6.0