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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2015	Nov. 02, 2015
Document and Entity Information
Entity Registrant Name	TC PIPELINES LP
Entity Central Index Key	0001075607
Document Type	10-Q
Document Period End Date	Sep. 30, 2015
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		64,179,181
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3

CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Transmission revenues	$ 83	$ 80		$ 255	$ 249
Equity earnings from unconsolidated affiliates (Note 4)	17	15		63	66
Operation and maintenance expenses	(12)	(14)		(36)	(38)
Property taxes	(5)	(5)		(16)	(17)
General and administrative	(1)	(5)		(5)	(8)
Depreciation	(21)	(21)		(63)	(64)
Financial charges and other (Note 14)	(12)	(11)		(41)	(37)
Net income	49	39		157	151
Net income attributable to non-controlling interests		8		7	26
Net income attributable to controlling interests	49	31		150	125
Calculation of net income attributable to common units
Net income attributable to controlling interests	49	31		150	125
Net income allocated to the General Partner, including incentive distributions	2	1		5	3
Class B units
Calculation of net income attributable to common units
Net income attributable to limited partners (Note 8)	2		$ 2	2
Common units
Calculation of net income attributable to common units
Net income attributable to limited partners (Note 8)	$ 45	$ 30		$ 143	$ 122
Weighted average common units outstanding (millions) - basic (in units)	64.0	62.6		63.8	62.4
Weighted average common units outstanding (millions) - diluted (in units)	64.0	62.6		63.8	62.4
Net income per common unit (Note 8) - basic (in dollars per unit)	$ 0.70	$ 0.48		$ 2.23	$ 1.96
Net income per common unit (Note 8) - diluted (in dollars per unit)	$ 0.70	$ 0.48		$ 2.23	$ 1.96
Common units outstanding, end of period (millions) (in units)	64.0	63.6	64.0	64.0	63.6

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Net income	$ 49	$ 39	$ 157	$ 151
Other comprehensive income
Change in fair value of cash flow hedges (Note 12)	(1)		(2)	(1)
Comprehensive income	48	39	155	150
Comprehensive income attributable to non-controlling interests		8	7	26
Comprehensive income attributable to controlling interests	$ 48	$ 31	$ 148	$ 124

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Current Assets
Cash and cash equivalents	$ 28	$ 26
Accounts receivable and other (Note 13)	31	35
Inventories	7	7
Total current assets	66	68
Investments in unconsolidated affiliates (Note 4)	1,151	1,177
Plant, property and equipment (Net of $790 accumulated depreciation; 2014 - $737	1,953	1,968
Goodwill	130	130
Other assets	8	6
Total assets	3,308	3,349
Current Liabilities
Accounts payable and accrued liabilities	30	23
Accounts payable to affiliates (Note 11)	8	15
Accrued interest	12	4
Short-term loan (Note 5)		170
Current portion of long-term debt (Note 5)	14	79
Total current liabilities	64	291
Long-term debt (Note 5)	1,890	1,446
Other liabilities	27	26
Total liabilities	1,981	1,763
Partners' Equity
General partner	29	29
Accumulated other comprehensive loss	(4)	(2)
Controlling interests	1,327	1,352
Non-controlling interests		234
Total partners' equity	1,327	1,586
Total liabilities and partners' equity	3,308	3,349
Common units
Partners' Equity
Limited partner	1,205	$ 1,325
Class B units
Partners' Equity
Limited partner	$ 97

CONSOLIDATED BALANCE SHEET (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
CONSOLIDATED BALANCE SHEETS
Accumulated depreciation	$ 790	$ 737

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash Generated From Operations
Net income	$ 157	$ 151
Depreciation	63	64
Amortization of debt issue costs (Note 14)	1	1
Accruals for costs related to the 2014 Bison Acquisition		2
Change in other liabilities		1
Equity allowance for funds used during construction	(1)
Change in operating working capital (Note 10)	9	36
Total cash generated from operations	229	255
Investing Activities
Investment in Great Lakes	(4)	(4)
Adjustment to the 2013 acquisition (Note 11)		(25)
Acquisition of the remaining 30 percent interest in GTN (Note 6)	(264)
Capital expenditures	(45)	(8)
Other	1	1
Total investing activities	(282)	(11)
Financing Activities
Distributions paid (Note 9)	(169)	(157)
Distributions paid to non-controlling interests	(9)	(42)
ATM Equity issuance, net (Note 7)	26	73
Equity contribution by the General Partner (Note 6)	2
Long-term debt issued, net of discount	598	15
Long-term debt repaid	(390)	(60)
Debt issuance costs	(3)
Total financing activities	55	(171)
Increase/(decrease) in cash and cash equivalents	2	73
Cash and cash equivalents, beginning of period	26	25
Cash and cash equivalents, end of period	28	98
Northern Border
Investing Activities
Cumulative distributions in excess of equity earnings	18	15
Great Lakes
Investing Activities
Cumulative distributions in excess of equity earnings	$ 12	$ 10

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical)	Apr. 01, 2015
GTN \| Transaction between entities under common control \| Former parent, TransCanada subsidiaries
GTN ACQUISITION
Business Acquisition, Percentage of Voting Interests Acquired	30.00%

CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY - 9 months ended Sep. 30, 2015 - USD ($)
shares in Millions, $ in Millions

Limited Partners

Common units

ATM Equity Issuance Program

Limited Partners

Common units

Limited Partners

Class B units

Unit issuances

Limited Partners

Class B units

General Partner

ATM Equity Issuance Program

General Partner

Accumulated Other Comprehensive Loss

Class B units

Unit issuances

Non-controlling interests

ATM Equity Issuance Program

Total

Balance as of beginning year at Dec. 31, 2014

$ 1,325

$ 29

$ (2)

$ 234

$ 1,586

Partners' Equity at beginning of year (in units) at Dec. 31, 2014

63.6

Increase (Decrease) in Partners' Equity

Net income

$ 143

$ 2

157

Other comprehensive loss

(2)

Equity issuance, net (Note 7); Unit Issuances (Note 6)

$ 25

$ 95

$ 1

$ 95

$ 26

Equity issuance (Note 7); Unit issuances (Note 6) (in units)

0.4

1.9

Acquisition of the remaining 30 percent interest in GTN (Note 6)

(124)

(3)

(232)

(359)

Equity contribution (Note 6)

Distributions paid

(164)

(5)

$ (9)

(178)

Balance as of end year at Sep. 30, 2015

$ 1,205

$ 97

$ 29

$ (4)

^[1]

$ 1,327

Partners' Equity at End of Year (in units) at Sep. 30, 2015

64.0

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 $1 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	9 Months Ended
	Sep. 30, 2015 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	$ 1

ORGANIZATION	9 Months Ended
ORGANIZATION	Sep. 30, 2015
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.

SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
SIGNIFICANT ACCOUNTING POLICIES	Sep. 30, 2015
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 nine months ended September 30, 2015 and 2014 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, 2014. 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 Note 2 of the financial statements in our Annual Report on Form 10-K for the year ended December 31, 2014. Certain items from that Note are repeated or updated below as necessary to assist in understanding the accompanying financial statements. (a) Basis of Presentation The Partnership accounts for business acquisitions between itself and TransCanada and its affiliates as transactions between entities under common control. Using this approach, the assets and liabilities of the acquired entities are recorded at TransCanada’s carrying value. In the event recasting is required, the Partnership’s historical financial information will be recast, except net income per common unit, to include the acquired entities for all periods presented. If the fair market value paid for the acquired entities is greater than the recorded net assets of the acquired entities, the excess purchase price paid is recorded as a reduction in Partners’ Equity. Similarly, if the fair market value paid for the acquired entities is less than the recorded net assets of the acquired entities, the excess of assets acquired is recorded as an increase in Partners’ Equity. The Partnership consolidates its investments in GTN, Bison, North Baja and Tuscarora, over which it is able to exercise control. To the extent there are interests owned by other parties, these interests are included in non-controlling interests. The Partnership uses the equity method of accounting for its investments in Northern Border and Great Lakes, over which it is able to exercise significant influence. (b) 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	9 Months Ended
ACCOUNTING PRONOUNCEMENTS	Sep. 30, 2015
ACCOUNTING PRONOUNCEMENTS
ACCOUNTING PRONOUNCEMENTS	NOTE 3ACCOUNTING PRONOUNCEMENTS Revenue from contracts with customers In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (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. The Partnership is currently evaluating the impact of the adoption of this ASU and has not yet determined the effect on its consolidated financial statements. Consolidation In February 2015, the FASB issued 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 is effective from January 1, 2016 and early application is permitted. Application of this amendment could be performed using a modified retrospective approach by recording a cumulative-effect adjustment to equity as of the beginning of the fiscal year of adoption. Alternatively, the amendment could be applied retrospectively. The Partnership is currently evaluating the impact of the adoption of this ASU and has not yet determined the effect on its consolidated financial statements. 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. The recognition and measurement for debt issuance costs would not be affected. This guidance is effective from January 1, 2016 and early application is permitted. This guidance should be adopted on a retrospective basis, wherein the balance sheet of each individual period presented would be adjusted to reflect the period-specific effects of applying the new guidance. The application of this amendment will result in a reclassification of debt issuance costs currently recorded in Other Assets to an offset of 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 is effective from January 1, 2016 and early application is permitted. This guidance should be adopted on a retrospective basis to all financial statements presented. The Partnership is currently evaluating the impact of the adoption of this ASU and has not yet determined the effect on its consolidated financial statements. 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 will be applied prospectively.

INVESTMENTS IN UNCONSOLIDATED AFFILIATES

9 Months Ended

Sep. 30, 2015

INVESTMENTS IN UNCONSOLIDATED AFFILIATES

INVESTMENTS IN UNCONSOLIDATED AFFILIATES

NOTE 4INVESTMENTS IN UNCONSOLIDATED AFFILIATES

Northern Border and Great Lakes are regulated by FERC and are operated by TransCanada. The Partnership uses the equity method of accounting for its interests in its equity investees.

	Ownership	Equity Earnings from Unconsolidated Affiliates				Investments in Unconsolidated Affiliates
	Interest at	Three months		Nine Months
(unaudited)	September 30,	ended September 30,		ended September 30,		September 30,	December 31,
(millions of dollars)	2015	2015	2014	2015	2014	2015	2014

Northern Border (a)	50%	16	14	50	53	487	505
Great Lakes	46.45%	1	1	13	13	664	672


		17	15	63	66	1,151	1,177

(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.

Northern Border

The Partnership does not have undistributed earnings from Northern Border for the nine months ended September 30, 2015 and 2014.

The summarized financial information for Northern Border is as follows:

(unaudited)
(millions of dollars)	September 30, 2015	December 31, 2014

ASSETS
Cash and cash equivalents	40	41
Other current assets	33	34
Plant, property and equipment, net	1,135	1,163
Other assets	18	34

	1,226	1,272


LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	50	64
Deferred credits and other	25	22
Long-term debt, including current maturities	411	411
Partners’ equity
Partners’ capital	742	777
Accumulated other comprehensive loss	(2)	(2)

	1,226	1,272

	Three months ended		Nine months ended

(unaudited)	September 30,		September 30,

(millions of dollars)	2015	2014	2015	2014


Transmission revenues	71	66	215	221
Operating expenses	(17)	(16)	(51)	(50)
Depreciation	(16)	(15)	(45)	(44)
Financial charges and other	(6)	(8)	(17)	(20)

Net income	32	27	102	107

Great Lakes

The Partnership made an equity contribution to Great Lakes of $4 million in the first quarter of 2015. 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 does not have undistributed earnings from Great Lakes for the nine months ended September 30, 2015 and 2014.

The summarized financial information for Great Lakes is as follows:

(unaudited)
(millions of dollars)	September 30, 2015	December 31, 2014

ASSETS
Current assets	67	66
Plant, property and equipment, net	730	748

	797	814




LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	48	38
Long-term debt, including current maturities	307	316
Partners’ equity	442	460

	797	814

	Three months ended		Nine months ended

(unaudited)	September 30,		September 30,

(millions of dollars)	2015	2014	2015	2014


Transmission revenues	29	29	105	106
Operating expenses	(15)	(14)	(40)	(38)
Depreciation	(7)	(7)	(21)	(21)
Financial charges and other	(5)	(6)	(17)	(19)
Net income	2	2	27	28

DEBT AND CREDIT FACILITIES

9 Months Ended

Sep. 30, 2015

DEBT AND CREDIT FACILITIES

DEBT AND CREDIT FACILITIES

NOTE 5DEBT AND CREDIT FACILITIES

(unaudited)
(millions of dollars)	September 30, 2015	December 31, 2014

Senior Credit Facility due 2017	190	330
2013 Term Loan Facility due 2018	500	500
Short Term Loan Facility due 2015	-	170
2015 Term Loan Facility due 2018	170	-
4.65% Unsecured Senior Notes due 2021, net of discount (2015 and 2014 – nil)	350	350
4.375% Unsecured Senior Notes due 2025, net of $1 million discount	349	-
5.09% Unsecured Senior Notes due 2015	-	75
5.29% Unsecured Senior Notes due 2020	100	100
5.69% Unsecured Senior Notes due 2035	150	150
Unsecured Term Loan Facility due 2019	75	-
3.82% Series D Senior Notes due 2017	20	20
	1,904	1,695
Less: current portion	14	249
	1,890	1,446

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 $190 million was outstanding at September 30, 2015 (December 31, 2014 - $330 million), leaving $310 million available for future borrowing.

The London Interbank Offered Rate (LIBOR) based interest rate on the Senior Credit Facility averaged 1.44 percent and 1.43 percent for the three and nine months ended September 30, 2015, respectively (2014 – 1.41 percent). The LIBOR-based interest rate was 1.45 percent at September 30, 2015 (December 31, 2014 – 1.41 percent).

The LIBOR-based interest rate on the 2013 Term Loan Facility averaged 1.44 percent for the both three and nine months ended September 30, 2015 (2014 – 1.41 percent). After hedging activity, the interest rate incurred on the 2013 Term Loan Facility averaged 1.85 percent and 1.84 percent for the three and nine months ended September 30, 2015, respectively (2014 – 1.83 percent). Prior to hedging activities, the LIBOR-based interest rate was 1.45 percent at September 30, 2015 (December 31, 2014 – 1.41 percent).

The LIBOR-based interest rate on the Short-Term Loan Facility averaged 1.32 percent and 1.31 percent for the three and nine months ended September 30, 2015, respectively and was 1.32 percent at September 30, 2015 (December 31, 2014 – 1.28 percent).

On September 30, 2015, the Partnership entered into an agreement for a $170 million term loan credit facility (2015 Term Loan Facility). The Partnership borrowed $170 million under the 2015 Term Loan Facility to refinance its Short-Term Loan Facility which matured on September 30, 2015. The 2015 Term Loan Facility matures on October 1, 2018. The LIBOR-based interest rate on the 2015 Term Loan Facility was 3.40 percent at September 30, 2015 and reduced to a LIBOR plus a margin of 1.15 percent on October 5, 2015.

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]). In the quarter in which an acquisition has occurred, and the two quarters following the acquisition, the allowable leverage ratio increases to 5.50 to 1.00. Thereafter, the ratio returns to 5.00 to 1.00. The allowable ratio for the quarter ended September 30, 2015 is 5.50 to 1.00. The leverage ratio was 4.71 to 1.00 as of September 30, 2015.

On March 13, 2015, the Partnership closed a $350 million public offering of senior unsecured notes bearing an interest rate of 4.375 percent maturing March 13, 2025. The net proceeds of $346 million were used to fund a portion of the acquisition of the remaining 30 percent interest in GTN (refer to Note 6) and to reduce the amount outstanding under our Senior Credit Facility. The indenture for the notes contains customary investment grade covenants.

On June 1, 2015, GTN’s 5.09 percent unsecured Senior Notes matured. Also, on June 1, 2015, GTN entered into a $75 million unsecured variable rate term loan facility (Unsecured Term Loan Facility), which requires yearly principal payments until its maturity on June 1, 2019. The variable interest is based on LIBOR plus an applicable margin. The LIBOR-based interest rate on the Unsecured Term Loan Facility for the three and nine months ended September 30, 2015 averaged 1.14 percent and was 1.15 percent at September 30, 2015. GTN’s Unsecured Senior Notes, along with this new 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 September 30, 2015 is 44 percent.

The 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.

At September 30, 2015, 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)

2015		4
2016		14
2017		212
2018		690
2019		35
2020		100
Thereafter		849

		1,904

GTN ACQUISITION

9 Months Ended

Sep. 30, 2015

GTN ACQUISITION

GTN ACQUISITION

NOTE 6GTN ACQUISITION

On April 1, 2015, the Partnership acquired the remaining 30 percent interest in GTN from a subsidiary of TransCanada (2015 GTN Acquisition), which resulted in GTN being wholly-owned by the Partnership. The total purchase price of the 2015 GTN Acquisition was $446 million plus the final purchase price adjustment of $11 million, for a total of $457 million. The purchase price consisted of $264 million in cash (including the final purchase price adjustment of $11 million), the assumption of $98 million in proportional GTN debt and the issuance of 1,900,000 new Class B units to TransCanada valued at $50 each, representing a limited partner interest in the Partnership with a total value of $95 million.

The Partnership funded the cash portion of the transaction using a portion of the proceeds received on our March 13, 2015 debt offering (refer to Note 5). The Class B units entitle TransCanada to a 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. Under the terms of the Partnership Agreement, the Class B distribution will be initially calculated to equal 30 percent of GTN’s distributable cash flow for the nine months ending December 31, 2015, less $15 million.

Prior to this transaction, the remaining 30 percent interest held by a subsidiary of TransCanada was reflected as a non-controlling interest in the Partnership’s consolidated financial statements. The 2015 Acquisition of this already-consolidated entity was accounted as a transaction between entities under common control, similar to a pooling of interests, whereby the acquired interest was recorded at TransCanada’s carrying value and the total excess purchase price paid was recorded as a reduction in Partners’ Equity.

The net purchase price was allocated as follows:

(millions of dollars)

Net Purchase Price (a)		359

Less: TransCanada’s carrying value of non-controlling interest at April 1, 2015		232

Excess purchase price (b)		127

(a)

Total purchase price of $457 million less the assumption of $98 million of proportional GTN debt by the Partnership.

(b)

The excess purchase price of $127 million was recorded as a reduction in Partners’ Equity.

Our General Partner also contributed approximately $2 million to maintain its effective 2 percent interest in the Partnership.

- Definition

The entire disclosure for a business combination (or series of individually immaterial business combinations) completed during the period, including background, timing, and recognized assets and liabilities. The disclosure may include leverage buyout transactions (as applicable).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1497-128463

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1490-128463

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1392-128463

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e7008-128479

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1486-128463

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=56956791&loc=d3e4845-128472

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1500-128463

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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+ Details

PARTNERS' EQUITY	9 Months Ended
PARTNERS' EQUITY	Sep. 30, 2015
PARTNERS' EQUITY
PARTNERS' EQUITY	NOTE 7PARTNERS’ EQUITY ATM equity issuance program (ATM program) For the nine months ended September 30, 2015, we issued 396,205 common units under our ATM program generating net proceeds of approximately $25 million, plus $1 million from the General Partner to maintain its effective two percent interest. The commissions to our sales agents for the nine months ended September 30, 2015 were approximately $256,000. The net proceeds were used for general partnership purposes. Issuance of Class B units On April 1, 2015, we issued Class B units to TransCanada to finance a portion of the 2015 GTN Acquisition. The Class B units entitle TransCanada to an annual distribution which is an amount based on 30 percent of cash distributions from GTN above certain annual thresholds (refer to Note 6). The Class B units contain no mandatory or optional redemption features and are also non-convertible, non-exchangeable, non-voting and rank equally with common units upon liquidation. The Class B units’ equity account will be increased by the excess of 30 percent of GTN’s distributions over the annual threshold until such amount is declared for distribution and paid in the first quarter beginning 2016 and annually thereafter.

NET INCOME PER COMMON UNIT

9 Months Ended

Sep. 30, 2015

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. Incentive distributions allocated to the General Partner for the three and nine months ended September 30, 2015, were $1 million and $2 million, respectively (2014 – nil).

The amount allocable to the Class B units in 2015 equals an amount based upon 30 percent of GTN’s distributable cash flow during the nine months ending December 31, 2015 less $15 million (refer to Note 6).

Net income per common unit was determined as follows:

	Three months ended		Nine months ended

(unaudited)	September 30,		September 30,

(millions of dollars, except per common unit amounts)	2015	2014	2015	2014


Net income attributable to controlling interests	49	31	150	125
Net income attributable to the General Partner	(1)	(1)	(3)	(3)
Incentive distributions attributable to the General Partner (a)	(1)	-	(2)	-
Net income attributable to the Class B units (b)	(2)	-	(2)	-

Net income attributable to common units	45	30	143	122

Weighted average common units outstanding (millions) – basic and diluted	64.0	62.6	63.8	62.4
Net income per common unit – basic and diluted	$ 0.70	$ 0.48	$ 2.23	$ 1.96

(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 was based from the Partnership’s available cash during the current reporting period, but declared and paid in the subsequent reporting period.

(b) As discussed in Notes 6 and 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 will allocate a portion of net income attributable to controlling interests to the Class B units upon 30 percent of GTN’s total distributable cash flows exceeding $15 million for the nine month period ending December 31, 2015.

During the six months ended September 30, 2015, 30 percent of GTN’s total distributable cash flow was $17 million. As a result, $2 million of net income attributable to controlling interests was allocated to the Class B units for both the three and nine months ended September 30, 2015.

CASH DISTRIBUTIONS	9 Months Ended
CASH DISTRIBUTIONS	Sep. 30, 2015
CASH DISTRIBUTIONS
CASH DISTRIBUTIONS	NOTE 9CASH DISTRIBUTIONS In the three and nine months ended September 30, 2015, the Partnership distributed $0.89 and $2.57 per common unit, respectively (2014 – $0.84 and $2.46 per common unit) for a total of $59 million and $169 million, respectively (2014 - $54 million and $157 million). The distributions paid in the three and nine months ended September 30, 2015 included an incentive distribution to the General Partner of approximately $0.9 million and $1.5 million, respectively (2014 - $0.3 million).

CHANGE IN OPERATING WORKING CAPITAL

9 Months Ended

Sep. 30, 2015

CHANGE IN OPERATING WORKING CAPITAL

CHANGE IN OPERATING WORKING CAPITAL

NOTE 10CHANGE IN OPERATING WORKING CAPITAL

(unaudited)	Nine months ended September 30,
(millions of dollars)	2015	2014

Change in accounts receivable and other	4	5
Change in accounts payable and accrued liabilities	4(a)	10
Change in accounts payable to affiliates	(7)	13
Change in accrued interest	8	8

Change in operating working capital	9	36

(a)

Excludes certain non-cash items primarily related to accruals of $3 million for construction of GTN’s Carty Lateral.

RELATED PARTY TRANSACTIONS

9 Months Ended

Sep. 30, 2015

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 nine months ended September 30, 2015, respectively (2014 – $1 million and $2 million).

As operator, 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 nine months ended September 30, 2015 and 2014 by TransCanada’s subsidiaries and amounts payable to TransCanada’s subsidiaries at September 30, 2015 and December 31, 2014 are summarized in the following tables:

	Three months ended		Nine months ended
(unaudited)	September 30,		September 30,
(millions of dollars)	2015	2014	2015	2014

Capital and operating costs charged by TransCanada’s subsidiaries to:
Great Lakes (a)	7	7	21	22
Northern Border (a)	10	9	26	26
GTN (a)	8	8	22	21
Bison (a)	1	2	3	4
North Baja	1	1	4	3
Tuscarora	1	1	3	3
Impact on the Partnership’s net income:
Great Lakes	3	3	9	10
Northern Border	3	4	10	11
GTN (b)	6	5	17	14
Bison(c)	1	1	3	3
North Baja	1	1	4	3
Tuscarora	1	1	3	3

(a)

Represents 100 percent of the costs.

(b)

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

(c)

In October 2014, the Partnership acquired the remaining 30 percent interest in Bison.


(unaudited)
(millions of dollars)	September 30, 2015	December 31, 2014

Amount payable to TransCanada’s subsidiaries for costs charged in the period by:
Great Lakes (a)	5	9
Northern Border (a)	7	10
GTN	5	10
Bison	1	2
North Baja	1	1
Tuscarora	1	1

(a)

Represents 100 percent of the costs.

Great Lakes’ earns revenues from TransCanada and its affiliates under transportation contracts on multiple paths at various rates. Great Lakes earned $18 million and $65 million of transportation revenues under these contracts for the three and nine months ended September 30, 2015, respectively (2014 - $13 million and $48 million). These amounts represent 62 percent of total revenues earned by Great Lakes for the three and nine months ended September 30, 2015, respectively (2014 – 46 percent). Great Lakes also earned nil and $1 million of affiliated rental revenue for the three and nine months ended September 30, 2015, respectively (2014 – nil and $1 million).

Revenue from TransCanada and its affiliates of $9 million and $31 million are included in the Partnership’s equity earnings from Great Lakes for the three and nine months ended September 30, 2015, respectively (2014 - $6 million and $23 million). At September 30, 2015, $30 million was included in Great Lakes’ receivables in regards to the transportation contracts with TransCanada and its affiliates (December 31, 2014 - $15 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 will recognize the deferred transportation revenue of approximately $23 million in the fourth quarter of 2015.

In April 2014, the Partnership paid $25 million to a subsidiary of TransCanada as additional consideration on the 2013 Acquisition. The additional consideration paid was due to the transportation service agreement executed by Portland General Electric Company with GTN relating to the Carty Lateral project.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References + Details

FAIR VALUE MEASUREMENTS

9 Months Ended

Sep. 30, 2015

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.

The estimated fair value of the Partnership’s debt as at September 30, 2015 and December 31, 2014 are as follows:

(unaudited)	September 30, 2015		December 31, 2014
(millions of dollars)	Carrying Value	Fair Value	Carrying Value	Fair Value

Senior Credit Facility due 2017	190	190	330	330
2013 Term Loan Facility due 2018	500	500	500	500
Short-Term Loan Facility due 2015	-	-	170	170
2015 Term Loan due 2018	170	170	-	-
4.65% Senior Notes due 2021, net	350	347	350	375
4.375% Senior Notes due 2025, net	349	330	-	-
5.09% Unsecured Senior Notes due 2015	-	-	75	76
Unsecured Term Loan facility due 2019	75	75	-	-
5.29% Unsecured Senior Notes due 2020	100	109	100	111
5.69% Unsecured Senior Notes due 2035	150	158	150	168
3.82% Series D Senior Notes due 2017	20	21	20	21

	1,904	1,900	1,695	1,751

Long-term debt is recorded at amortized cost and classified in Level II of the fair value hierarchy for fair value disclosure purposes. Interest rate derivative assets and liabilities are classified in Level II for all periods presented where the fair value is determined by using valuation techniques that refer to observable market data or estimated market prices.

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 $150 million of the variable-rate 2013 Term Loan Facility with interest rate swaps effective September 3, 2013 and maturing July 1, 2018, at a weighted average fixed interest rate of 2.79 percent. At September 30, 2015, the fair value of the interest rate swaps accounted for as cash flow hedges was a liability of $3 million (both on a gross and net basis) (December 31, 2014 - $1 million). The Partnership did not record any amounts in net income related to ineffectiveness for interest rate hedges for the three and nine months ended September 30, 2015 and 2014. The change in fair value of interest rate derivative instruments recognized in other comprehensive income was a loss of $1 million and $2 million for the three and nine months ended September 30, 2015, respectively (2014 – nil and a loss of $1 million). For the three and nine months ended September 30, 2015, the net realized loss related to the interest rate swaps was $1 million and $2 million, respectively, and was included in financial charges and other (2014 – $1 million and $2 million) (refer to Note 14).

The Partnership has no master netting agreements; however, contracts contain 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 September 30, 2015 and December 31, 2014.

ACCOUNTS RECEIVABLE AND OTHER

9 Months Ended

Sep. 30, 2015

ACCOUNTS RECEIVABLE AND OTHER

ACCOUNTS RECEIVABLE AND OTHER

NOTE 13ACCOUNTS RECEIVABLE AND OTHER

(unaudited)
(millions of dollars)	September 30, 2015	December 31, 2014

Trade accounts receivable, net of allowance of nil	27	30
Accounts receivable from affiliates	1	1
Other	3	4

	31	35

FINANCIAL CHARGES AND OTHER

9 Months Ended

Sep. 30, 2015

FINANCIAL CHARGES AND OTHER

FINANCIAL CHARGES AND OTHER

NOTE 14FINANCIAL CHARGES AND OTHER

	Three months ended		Nine months ended
(unaudited)	September 30,		September 30,
(millions of dollars)	2015	2014	2015	2014

Interest Expense	15	11	43	35
Amortization of debt issue costs	-	-	1	1
Net realized loss related to the interest rate swaps	1	1	2	2
Other Income	(4)	(1)	(5)	(1)

	12	11	41	37

CONTINGENCIES	9 Months Ended
CONTINGENCIES	Sep. 30, 2015
CONTINGENCIES
CONTINGENCIES	NOTE 15CONTINGENCIES 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 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. The Partnership intends to defend vigorously against the claims asserted.

- 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
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-Name Accounting Standards Codification
-Topic 450
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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+ Details

SUBSEQUENT EVENTS	9 Months Ended
SUBSEQUENT EVENTS	Sep. 30, 2015
SUBSEQUENT EVENTS
SUBSEQUENT EVENTS	NOTE 16SUBSEQUENT EVENTS Management of the Partnership has reviewed subsequent events through November 6, 2015, 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 October 22, 2015, the board of directors of our General Partner declared the Partnership’s third quarter 2015 cash distribution in the amount of $0.89 per common unit payable on November 13, 2015 to unitholders of record as of November 3, 2015. Northern Border declared its third quarter 2015 distribution of $45 million on October 23, 2015, of which the Partnership will receive its 50 percent share or $23 million on November 2, 2015. Great Lakes declared its third quarter 2015 distribution of $7 million on October 23, 2015, of which the Partnership will receive its 46.45 percent share or $3 million on November 2, 2015. On October 9, 2015 Northern Border closed on the renewal and extension of its $200 million revolving credit facility that was to expire in 2016 for an additional five years, maturing October 9, 2020. On November 5, 2015, we entered into an agreement with TransCanada to acquire a 49.9 percent interest in the Portland Natural Gas Transmission System (PNGTS) for $223 million including approximately $35 million in proportionate PNGTS debt (PNGTS Acquisition). PNGTS is a high-capacity, high-pressure interstate natural gas pipeline which began serving New England’s energy needs in March, 1999. The pipeline connects with the TransQuebec and Maritimes Pipeline at the Canadian border and shares facilities with the Maritimes and Northeast Pipeline from Westbrook, Maine to a connection with the Tennessee Gas Pipeline System near Boston, MA. 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 transaction is expected to close at the end of 2015. The Partnership plans to finance the acquisition with a combination of debt and equity. The transaction was approved by the Board of Directors of the general partner, following approval and recommendation from the Board’s conflicts committee, which is comprised entirely of independent directors.

SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
SIGNIFICANT ACCOUNTING POLICIES (Policies)	Sep. 30, 2015
SIGNIFICANT ACCOUNTING POLICIES
Basis of Presentation - Transactions between entities under common control	(a) Basis of Presentation The Partnership accounts for business acquisitions between itself and TransCanada and its affiliates as transactions between entities under common control. Using this approach, the assets and liabilities of the acquired entities are recorded at TransCanada’s carrying value. In the event recasting is required, the Partnership’s historical financial information will be recast, except net income per common unit, to include the acquired entities for all periods presented. If the fair market value paid for the acquired entities is greater than the recorded net assets of the acquired entities, the excess purchase price paid is recorded as a reduction in Partners’ Equity. Similarly, if the fair market value paid for the acquired entities is less than the recorded net assets of the acquired entities, the excess of assets acquired is recorded as an increase in Partners’ Equity.
Basis of Presentation - Consolidation	(a) Basis of Presentation The Partnership consolidates its investments in GTN, Bison, North Baja and Tuscarora, over which it is able to exercise control. To the extent there are interests owned by other parties, these interests are included in non-controlling interests. The Partnership uses the equity method of accounting for its investments in Northern Border and Great Lakes, over which it is able to exercise significant influence.
Use of Estimates	(b) 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.

INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Tables)

9 Months Ended

Sep. 30, 2015

INVESTMENTS IN UNCONSOLIDATED AFFILIATES

Schedule of interests in equity investees

	Ownership	Equity Earnings from Unconsolidated Affiliates				Investments in Unconsolidated Affiliates
	Interest at	Three months		Nine Months
(unaudited)	September 30,	ended September 30,		ended September 30,		September 30,	December 31,
(millions of dollars)	2015	2015	2014	2015	2014	2015	2014

Northern Border (a)	50%	16	14	50	53	487	505
Great Lakes	46.45%	1	1	13	13	664	672


		17	15	63	66	1,151	1,177

Northern Border

Investments in unconsolidated affiliates

Summarized financial information for equity investees

(unaudited)
(millions of dollars)		September 30, 2015		December 31, 2014

ASSETS
Cash and cash equivalents		40		41
Other current assets		33		34
Plant, property and equipment, net		1,135		1,163
Other assets		18		34

		1,226		1,272


LIABILITIES AND PARTNERS’ EQUITY
Current liabilities		50		64
Deferred credits and other		25		22
Long-term debt, including current maturities		411		411
Partners’ equity
Partners’ capital		742		777
Accumulated other comprehensive loss		(2)		(2)

		1,226		1,272

	Three months ended				Nine months ended

(unaudited)	September 30,				September 30,

(millions of dollars)	2015		2014		2015	2014


Transmission revenues	71		66		215	221
Operating expenses	(17)		(16)		(51)	(50)
Depreciation	(16)		(15)		(45)	(44)
Financial charges and other	(6)		(8)		(17)	(20)

Net income	32		27		102	107

Great Lakes

Investments in unconsolidated affiliates

Summarized financial information for equity investees

(unaudited)
(millions of dollars)	September 30, 2015	December 31, 2014

ASSETS
Current assets	67	66
Plant, property and equipment, net	730	748

	797	814




LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	48	38
Long-term debt, including current maturities	307	316
Partners’ equity	442	460

	797	814

	Three months ended		Nine months ended

(unaudited)	September 30,		September 30,

(millions of dollars)	2015	2014	2015	2014


Transmission revenues	29	29	105	106
Operating expenses	(15)	(14)	(40)	(38)
Depreciation	(7)	(7)	(21)	(21)
Financial charges and other	(5)	(6)	(17)	(19)
Net income	2	2	27	28

DEBT AND CREDIT FACILITIES (Tables)

9 Months Ended

Sep. 30, 2015

DEBT AND CREDIT FACILITIES

Schedule of debt and credit facilities

(unaudited)
(millions of dollars)	September 30, 2015	December 31, 2014

Senior Credit Facility due 2017	190	330
2013 Term Loan Facility due 2018	500	500
Short Term Loan Facility due 2015	-	170
2015 Term Loan Facility due 2018	170	-
4.65% Unsecured Senior Notes due 2021, net of discount (2015 and 2014 – nil)	350	350
4.375% Unsecured Senior Notes due 2025, net of $1 million discount	349	-
5.09% Unsecured Senior Notes due 2015	-	75
5.29% Unsecured Senior Notes due 2020	100	100
5.69% Unsecured Senior Notes due 2035	150	150
Unsecured Term Loan Facility due 2019	75	-
3.82% Series D Senior Notes due 2017	20	20
	1,904	1,695
Less: current portion	14	249
	1,890	1,446

Schedule of principal repayments required on debt

(unaudited)
(millions of dollars)

2015		4
2016		14
2017		212
2018		690
2019		35
2020		100
Thereafter		849

		1,904

GTN ACQUISITION (Tables)

9 Months Ended

Sep. 30, 2015

GTN

GTN ACQUISITION

Schedule of purchase price

(millions of dollars)

Net Purchase Price (a)		359

Less: TransCanada’s carrying value of non-controlling interest at April 1, 2015		232

Excess purchase price (b)		127

(a)

Total purchase price of $457 million less the assumption of $98 million of proportional GTN debt by the Partnership.

(b)

The excess purchase price of $127 million was recorded as a reduction in Partners’ Equity.

NET INCOME PER COMMON UNIT (Tables)

9 Months Ended

Sep. 30, 2015

NET INCOME PER COMMON UNIT

Schedule of net income per common unit

	Three months ended		Nine months ended

(unaudited)	September 30,		September 30,

(millions of dollars, except per common unit amounts)	2015	2014	2015	2014


Net income attributable to controlling interests	49	31	150	125
Net income attributable to the General Partner	(1)	(1)	(3)	(3)
Incentive distributions attributable to the General Partner (a)	(1)	-	(2)	-
Net income attributable to the Class B units (b)	(2)	-	(2)	-

Net income attributable to common units	45	30	143	122

Weighted average common units outstanding (millions) – basic and diluted	64.0	62.6	63.8	62.4
Net income per common unit – basic and diluted	$ 0.70	$ 0.48	$ 2.23	$ 1.96

(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 was based from the Partnership’s available cash during the current reporting period, but declared and paid in the subsequent reporting period.

(b)

As discussed in Notes 6 and 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 will allocate a portion of net income attributable to controlling interests to the Class B units upon 30 percent of GTN’s total distributable cash flows exceeding $15 million for the nine month period ending December 31, 2015.

CHANGE IN OPERATING WORKING CAPITAL (Tables)

9 Months Ended

Sep. 30, 2015

CHANGE IN OPERATING WORKING CAPITAL

Summary of change in operating working capital

(unaudited)	Nine months ended September 30,
(millions of dollars)	2015	2014

Change in accounts receivable and other	4	5
Change in accounts payable and accrued liabilities	4(a)	10
Change in accounts payable to affiliates	(7)	13
Change in accrued interest	8	8

Change in operating working capital	9	36

(a)

Excludes certain non-cash items primarily related to accruals of $3 million for construction of GTN’s Carty Lateral.

RELATED PARTY TRANSACTIONS (Tables)

9 Months Ended

Sep. 30, 2015

RELATED PARTY TRANSACTIONS

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

	Three months ended		Nine months ended
(unaudited)	September 30,		September 30,
(millions of dollars)	2015	2014	2015	2014

Capital and operating costs charged by TransCanada’s subsidiaries to:
Great Lakes (a)	7	7	21	22
Northern Border (a)	10	9	26	26
GTN (a)	8	8	22	21
Bison (a)	1	2	3	4
North Baja	1	1	4	3
Tuscarora	1	1	3	3
Impact on the Partnership’s net income:
Great Lakes	3	3	9	10
Northern Border	3	4	10	11
GTN (b)	6	5	17	14
Bison(c)	1	1	3	3
North Baja	1	1	4	3
Tuscarora	1	1	3	3

(a)

Represents 100 percent of the costs.

(b)

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

(c)

In October 2014, the Partnership acquired the remaining 30 percent interest in Bison.

Summary of amount payable to related party for costs charged


(unaudited)
(millions of dollars)	September 30, 2015	December 31, 2014

Amount payable to TransCanada’s subsidiaries for costs charged in the period by:
Great Lakes (a)	5	9
Northern Border (a)	7	10
GTN	5	10
Bison	1	2
North Baja	1	1
Tuscarora	1	1

(a)

Represents 100 percent of the costs.

FAIR VALUE MEASUREMENTS (Tables)

9 Months Ended

Sep. 30, 2015

FAIR VALUE MEASUREMENTS

Schedule of estimated fair value of debt

(unaudited)	September 30, 2015		December 31, 2014
(millions of dollars)	Carrying Value	Fair Value	Carrying Value	Fair Value

Senior Credit Facility due 2017	190	190	330	330
2013 Term Loan Facility due 2018	500	500	500	500
Short-Term Loan Facility due 2015	-	-	170	170
2015 Term Loan due 2018	170	170	-	-
4.65% Senior Notes due 2021, net	350	347	350	375
4.375% Senior Notes due 2025, net	349	330	-	-
5.09% Unsecured Senior Notes due 2015	-	-	75	76
Unsecured Term Loan facility due 2019	75	75	-	-
5.29% Unsecured Senior Notes due 2020	100	109	100	111
5.69% Unsecured Senior Notes due 2035	150	158	150	168
3.82% Series D Senior Notes due 2017	20	21	20	21

	1,904	1,900	1,695	1,751

ACCOUNTS RECEIVABLE AND OTHER (Tables)

9 Months Ended

Sep. 30, 2015

ACCOUNTS RECEIVABLE AND OTHER

Schedule of accounts receivable and other

(unaudited)
(millions of dollars)	September 30, 2015	December 31, 2014

Trade accounts receivable, net of allowance of nil	27	30
Accounts receivable from affiliates	1	1
Other	3	4

	31	35

FINANCIAL CHARGES AND OTHER (Tables)

9 Months Ended

Sep. 30, 2015

FINANCIAL CHARGES AND OTHER

Schedule of components of financial charges and other

	Three months ended		Nine months ended
(unaudited)	September 30,		September 30,
(millions of dollars)	2015	2014	2015	2014

Interest Expense	15	11	43	35
Amortization of debt issue costs	-	-	1	1
Net realized loss related to the interest rate swaps	1	1	2	2
Other Income	(4)	(1)	(5)	(1)

	12	11	41	37

INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended
	Apr. 30, 2006	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Investments in unconsolidated affiliates
Equity Earnings from Unconsolidated Affiliates		$ 17		$ 15	$ 63	$ 66
Investments in Unconsolidated Affiliates		$ 1,151			1,151		$ 1,177
Equity contribution					$ 4	4
Great Lakes
Investments in unconsolidated affiliates
Total cash call issued to fund debt repayment			$ 9
Northern Border
Investments in unconsolidated affiliates
Ownership interest (as a percent)		50.00%			50.00%
Equity Earnings from Unconsolidated Affiliates		$ 16		14	$ 50	53
Investments in Unconsolidated Affiliates		487			487		505
Amortization period of transaction fee	12 years
Transaction fee	$ 10
Additional ownership interest acquired (as a percent)	20.00%
Assets
Cash and cash equivalents		40			40		41
Other current assets		33			33		34
Plant, property and equipment, net		1,135			1,135		1,163
Other assets		18			18		34
Assets, total		1,226			1,226		1,272
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		50			50		64
Deferred credits and other		25			25		22
Long-term debt, including current maturities		411			411		411
Partners' equity
Partners' equity		742			742		777
Accumulated other comprehensive loss		(2)			(2)		(2)
Liabilities and Partners' Equity, total		1,226			1,226		1,272
Revenues (expenses)
Transmission revenues		71		66	215	221
Operating expenses		(17)		(16)	(51)	(50)
Depreciation		(16)		(15)	(45)	(44)
Financial charges and other		(6)		(8)	(17)	(20)
Net income		$ 32		27	$ 102	107
Great Lakes
Investments in unconsolidated affiliates
Ownership interest (as a percent)		46.45%	46.45%		46.45%
Equity Earnings from Unconsolidated Affiliates		$ 1		1	$ 13	13
Investments in Unconsolidated Affiliates		664			664		672
Equity contribution			$ 4
Assets
Current assets		67			67		66
Plant, property and equipment, net		730			730		748
Assets, total		797			797		814
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		48			48		38
Long-term debt, including current maturities		307			307		316
Partners' equity
Partners' equity		442			442		460
Liabilities and Partners' Equity, total		797			797		$ 814
Revenues (expenses)
Transmission revenues		29		29	105	106
Operating expenses		(15)		(14)	(40)	(38)
Depreciation		(7)		(7)	(21)	(21)
Financial charges and other		(5)		(6)	(17)	(19)
Net income		$ 2		$ 2	$ 27	$ 28

DEBT AND CREDIT FACILITIES (Details) - USD ($)				3 Months Ended		4 Months Ended	9 Months Ended
DEBT AND CREDIT FACILITIES (Details) - USD ($)	Oct. 05, 2015	Sep. 30, 2015	Mar. 13, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 29, 2015	Jun. 01, 2015	Apr. 01, 2015	Dec. 31, 2014
Credit facilities, short-term loan facility and long-term debt
Credit facilities and long-term debt		$ 1,904,000,000		$ 1,904,000,000		$ 1,904,000,000	$ 1,904,000,000
Short-term loan												$ 170,000,000
Total credit facilities, short-term loan facility and long-term debt		1,904,000,000		1,904,000,000		1,904,000,000	1,904,000,000					1,695,000,000
Less: current portion		14,000,000		14,000,000		14,000,000	14,000,000					249,000,000
Long-term debt		$ 1,890,000,000		$ 1,890,000,000		$ 1,890,000,000	1,890,000,000					1,446,000,000
Net proceeds							$ 598,000,000	$ 15,000,000
GTN \| Former parent, TransCanada subsidiaries \| Transaction between entities under common control
Credit facilities, short-term loan facility and long-term debt
Interest acquired by Partnership (as a percent)											30.00%
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)		4.71%		4.71%		4.71%	4.71%
Senior Credit Facility and the Term Loan Facilities due in 2018 \| Maximum
Credit facilities, short-term loan facility and long-term debt
Leverage ratio, covenant (as a percent)				5.50%
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 \| Maximum
Credit facilities, short-term loan facility and long-term debt
Leverage ratio, covenant (as a percent)							5.50%
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)							5.00%
Term loan \| Short-Term Loan Facility due 2015
Credit facilities, short-term loan facility and long-term debt
Short-term loan		$ 0		$ 0		$ 0	$ 0					$ 170,000,000
Term loan \| Short-Term Loan Facility due 2015 \| LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt average interest rate (as a percent)				1.32%			1.31%
Debt interest rate, at period end (as a percent)									1.32%			1.28%
Revolving credit facility \| Senior Credit Facility due 2017
Credit facilities, short-term loan facility and long-term debt
Credit facilities and long-term debt		190,000,000		$ 190,000,000		190,000,000	$ 190,000,000					$ 330,000,000
Maximum borrowing capacity		500,000,000		500,000,000		500,000,000	500,000,000
Amount outstanding under credit facility		190,000,000		190,000,000		190,000,000	190,000,000					$ 330,000,000
Remaining borrowing capacity		$ 310,000,000		$ 310,000,000		$ 310,000,000	$ 310,000,000
Revolving credit facility \| Senior Credit Facility due 2017 \| LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt average interest rate (as a percent)				1.44%	1.41%		1.43%	1.41%
Debt interest rate, at period end (as a percent)		1.45%		1.45%		1.45%	1.45%					1.41%
Term loan \| 2013 Term Loan Facility due 2018
Credit facilities, short-term loan facility and long-term debt
Credit facilities and long-term debt		$ 500,000,000		$ 500,000,000		$ 500,000,000	$ 500,000,000					$ 500,000,000
Term loan \| 2013 Term Loan Facility due 2018 \| LIBOR borrowings \| LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt average interest rate (as a percent)				1.44%	1.41%		1.44%	1.41%
Debt interest rate, at period end (as a percent)		1.45%		1.45%		1.45%	1.45%					1.41%
Term loan \| 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
Debt average interest rate (as a percent)				1.85%	1.83%		1.84%	1.83%
Term loan \| 2015 Term Loan Facility due 2018
Credit facilities, short-term loan facility and long-term debt
Credit facilities and long-term debt		$ 170,000,000		$ 170,000,000		$ 170,000,000	$ 170,000,000
Amount of debt		170,000,000		$ 170,000,000		$ 170,000,000	$ 170,000,000
Amount borrowed		$ 170,000,000
Term loan \| 2015 Term Loan Facility due 2018 \| LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end (as a percent)		3.40%		3.40%		3.40%	3.40%
Basis spread on variable rate (as a percent)	1.15%
Unsecured debt \| 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%	4.65%					4.65%
Discount		$ 0		$ 0		$ 0	$ 0					$ 0
Credit facilities and long-term debt		$ 350,000,000		$ 350,000,000		$ 350,000,000	$ 350,000,000					$ 350,000,000
Unsecured debt \| 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%		4.375%	4.375%
Discount		$ 1,000,000		$ 1,000,000		$ 1,000,000	$ 1,000,000
Credit facilities and long-term debt		$ 349,000,000		$ 349,000,000		$ 349,000,000	$ 349,000,000
Amount of debt			$ 350,000,000
Net proceeds			$ 346,000,000
Unsecured debt \| 5.09% Senior Notes due 2015
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)												5.09%
Credit facilities and long-term debt												$ 75,000,000
Unsecured debt \| 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%	5.29%					5.29%
Credit facilities and long-term debt		$ 100,000,000		$ 100,000,000		$ 100,000,000	$ 100,000,000					$ 100,000,000
Unsecured debt \| 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%	5.69%					5.69%
Credit facilities and long-term debt		$ 150,000,000		$ 150,000,000		$ 150,000,000	$ 150,000,000					$ 150,000,000
Unsecured debt \| Term Loan Facility due 2019
Credit facilities, short-term loan facility and long-term debt
Credit facilities and long-term debt		$ 75,000,000		$ 75,000,000		$ 75,000,000	$ 75,000,000
Secured debt \| 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%	3.82%					3.82%
Credit facilities and long-term debt		$ 20,000,000		$ 20,000,000		$ 20,000,000	$ 20,000,000					$ 20,000,000
GTN
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization, actual		44.00%		44.00%		44.00%	44.00%
GTN \| Unsecured debt \| 5.09% Senior Notes due 2015
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)												5.09%
GTN \| Unsecured debt \| 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%
GTN \| Unsecured debt \| Term Loan Facility due 2019 \| LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt average interest rate (as a percent)				1.14%			1.14%
Debt interest rate, at period end (as a percent)		1.15%		1.15%		1.15%	1.15%
Amount of debt										$ 75,000,000
GTN \| Senior Notes \| Maximum
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization, covenant							70.00%

DEBT AND CREDIT FACILITIES (Details 2) $ in Millions	Sep. 30, 2015 USD ($)
Principal repayments required on debt
2015	$ 4
2016	14
2017	212
2018	690
2019	35
2020	100
Thereafter	849
Total debt	$ 1,904

GTN ACQUISITION (Details) - USD ($)		6 Months Ended	9 Months Ended
GTN ACQUISITION (Details) - USD ($)	Apr. 01, 2015	Sep. 30, 2015	Sep. 30, 2015	Mar. 31, 2015
Acquisition
Total cash consideration			$ 264,000,000
GTN \| Former parent, TransCanada subsidiaries \| Transaction between entities under common control
Acquisition
Interest acquired (as a percent)	30.00%
Purchase price adjustments	$ 11,000,000
Purchase price	457,000,000
Total cash consideration	264,000,000
Assumption of proportional debt	98,000,000
GTN \| Former parent, TransCanada subsidiaries \| Transaction between entities under common control \| Previously reported
Acquisition
Purchase price	$ 446,000,000
Partnership interest \| Class B units \| GTN \| Former parent, TransCanada subsidiaries \| Transaction between entities under common control
Acquisition
Units issued (in units)	1,900,000
Value per unit (in dollars per unit)	$ 50
Equity issuance	$ 95,000,000
GTN \| Class B units \| TransCanada \| Distributions
Distributions
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 30 percent of GTN's annual distributions for payment to Class B units at specified percentage	$ 20,000,000
Percentage applied to 30 percent of GTN's distributions above threshold after March 31, 2020	25.00%
Percentage applied to GTN's distributable cash flow for the nine months ending December 31, 2015		30.00%
Prorated threshold of GTN's distributions for payment to Class B units		$ 15,000,000
TransCanada \| GTN
Noncontrolling interest
Remaining noncontrolling ownership interest (as a percent)				30.00%

GTN ACQUISITION (Details 2) - USD ($) $ in Millions		9 Months Ended
GTN ACQUISITION (Details 2) - USD ($) $ in Millions	Apr. 01, 2015	Sep. 30, 2015
Net purchase price allocation
Reduction in Partners' Equity		$ 359
GTN \| Former parent, TransCanada subsidiaries \| Transaction between entities under common control
Net purchase price allocation
Net Purchase Price	$ 359
Less: TransCanada's carrying value of non-controlling interest as April 1, 2015	232
Excess purchase price	127
Purchase price	457
Assumption of proportional debt	98
GTN \| Former parent, TransCanada subsidiaries \| Transaction between entities under common control \| Limited Partner and General Partner interests combined
Net purchase price allocation
Reduction in Partners' Equity	$ 127

GTN ACQUISITION (Details 3) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
GTN ACQUISITION (Details 3) - USD ($) $ in Millions	Apr. 02, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
GTN ACQUISITION
Equity contribution				$ 2
General Partner
GTN ACQUISITION
Equity contribution				$ 2
General Partner \| Partnership
GTN ACQUISITION
Equity contribution	$ 2
General Partner \| TC PipeLines GP, Inc.
GTN ACQUISITION
Ownership interest in the Partnership (as a percent)	2.00%	2.00%	2.00%	2.00%	2.00%

PARTNERS' EQUITY (Details) - USD ($)		3 Months Ended		9 Months Ended
PARTNERS' EQUITY (Details) - USD ($)	Apr. 02, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Partners' Equity
Equity contribution				$ 2,000,000
General Partner
Partners' Equity
Equity contribution				$ 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%	2.00%
ATM Equity Issuance Program \| Common units
Partners' Equity
Units sold				396,205
Net proceeds from public offering of common units				$ 25,000,000
Sales agent commissions				256,000
ATM Equity Issuance Program \| TC PipeLines GP, Inc. \| General Partner
Partners' Equity
Equity contribution				$ 1,000,000

PARTNERS' EQUITY (Details 2)	Apr. 01, 2015
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%

NET INCOME PER COMMON UNIT (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Apr. 02, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Partners' Equity
Incentive distributions allocated to the General Partner		$ 1		$ 2
TC PipeLines GP, Inc. \| General Partner
Partners' Equity
General partner interest (as a percent)	2.00%	2.00%	2.00%	2.00%	2.00%

NET INCOME PER COMMON UNIT (Details 2) - USD ($) $ / shares in Units, shares in Millions		3 Months Ended		6 Months Ended	9 Months Ended
	Apr. 01, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Net income per common unit
Net income attributable to controlling interests		$ 49,000,000	$ 31,000,000		$ 150,000,000	$ 125,000,000
Net income attributable to the General Partner		(1,000,000)	(1,000,000)		(3,000,000)	(3,000,000)
Incentive distributions attributable to the General Partner		(1,000,000)			(2,000,000)
Class B units
Net income per common unit
Net income allocated to limited partners		2,000,000		$ 2,000,000	2,000,000
Common units
Net income per common unit
Net income allocated to limited partners		$ 45,000,000	$ 30,000,000		$ 143,000,000	$ 122,000,000
Weighted average common units outstanding (millions) - basic (in units)		64.0	62.6		63.8	62.4
Weighted average common units outstanding (millions) - diluted (in units)		64.0	62.6		63.8	62.4
Net income per common unit - basic (in dollars per unit)		$ 0.70	$ 0.48		$ 2.23	$ 1.96
Net income per common unit - diluted (in dollars per unit)		$ 0.70	$ 0.48		$ 2.23	$ 1.96
GTN
Distributions
30% of GTN's distributable cash flow				$ 17,000,000
GTN \| Class B units \| TransCanada \| Distributions
Distributions
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 GTN's distributable cash flow for the nine months ending December 31, 2015				30.00%
Prorated threshold of GTN's distributions for payment to Class B units				$ 15,000,000

CASH DISTRIBUTIONS (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Common units
Distributions
Partnership distribution (in dollars per unit)	$ 0.89	$ 0.84	$ 2.57	$ 2.46
Limited Partner and General Partner interests combined \| Common units
Distributions
Partnership distribution	$ 59.0	$ 54.0	$ 169.0	$ 157.0
General Partner
Distributions
Incentive distribution paid to the General Partner	$ 0.9	$ 0.3	$ 1.5	$ 0.3

CHANGE IN OPERATING WORKING CAPITAL (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
CHANGE IN OPERATING WORKING CAPITAL
Change in accounts receivable and other	$ 4	$ 5
Change in accounts payable and accrued liabilities	4	10
Change in accounts payable to affiliates	(7)	13
Change in accrued interest	8	8
Change in operating working capital	$ 9	$ 36

CHANGE IN OPERATING WORKING CAPITAL (Details 2) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($)
GTN
Non-cash items
Accruals for capital expenditures	$ 3

RELATED PARTY TRANSACTIONS (Details) - USD ($) $ in Millions			1 Months Ended	3 Months Ended		4 Months Ended	9 Months Ended		12 Months Ended
	Oct. 15, 2015	Dec. 31, 2014	Apr. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	May 03, 2015	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Apr. 01, 2015	Oct. 01, 2014
Capital and operating costs charged to the pipeline systems and amount payable
Accounts payable to affiliates		$ 15.0		$ 8.0			$ 8.0		$ 15.0
Amount included in receivables from related party		1.0		1.0			1.0		1.0
Additional acquisition consideration relating to Carty Lateral project								$ 25.0
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	2.0
TransCanada's subsidiaries \| Great Lakes
Capital and operating costs charged to the pipeline systems and amount payable
Accounts payable to affiliates		9.0		5.0			5.0		9.0
Amount included in receivables from related party		$ 15.0		30.0			30.0		15.0
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	7.0		21.0	22.0
Impact on the Partnership's net income				$ 3.0	$ 3.0		$ 9.0	$ 10.0
Percentage of capital and operating costs charged		100.00%		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				$ 18.0	$ 13.0		$ 65.0	$ 48.0
TransCanada's subsidiaries \| Great Lakes \| Transportation contracts \| Total revenues \| Major customers
Capital and operating costs charged to the pipeline systems and amount payable
Percent of total revenues				62.00%	46.00%		62.00%	46.00%
TransCanada's subsidiaries \| Great Lakes \| Affiliated rental revenue
Capital and operating costs charged to the pipeline systems and amount payable
Revenues from related party				$ 0.0	$ 0.0		$ 1.0	$ 1.0
TransCanada's subsidiaries \| Northern Border
Capital and operating costs charged to the pipeline systems and amount payable
Accounts payable to affiliates		$ 10.0		7.0			7.0		10.0
TransCanada's subsidiaries \| Northern Border \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged				10.0	9.0		26.0	26.0
Impact on the Partnership's net income				$ 3.0	$ 4.0		$ 10.0	$ 11.0
Percentage of capital and operating costs charged		100.00%		100.00%	100.00%		100.00%	100.00%
TransCanada's subsidiaries \| GTN
Capital and operating costs charged to the pipeline systems and amount payable
Accounts payable to affiliates		$ 10.0		$ 5.0			$ 5.0		10.0
TransCanada's subsidiaries \| GTN \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged				8.0	$ 8.0		22.0	$ 21.0
Impact on the Partnership's net income				$ 6.0	$ 5.0		$ 17.0	$ 14.0
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
Accounts payable to affiliates		2.0		$ 1.0			$ 1.0		2.0
TransCanada's subsidiaries \| Bison \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged				1.0	$ 2.0		3.0	$ 4.0
Impact on the Partnership's net income				$ 1.0	$ 1.0		$ 3.0	$ 3.0
Percentage of capital and operating costs charged				100.00%	100.00%		100.00%	100.00%
TransCanada's subsidiaries \| North Baja Pipeline, LLC
Capital and operating costs charged to the pipeline systems and amount payable
Accounts payable to affiliates		1.0		$ 1.0			$ 1.0		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	$ 1.0		4.0	$ 3.0
Impact on the Partnership's net income				1.0	1.0		4.0	3.0
TransCanada's subsidiaries \| Tuscarora Gas Transmission Company
Capital and operating costs charged to the pipeline systems and amount payable
Accounts payable to affiliates		$ 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		3.0	3.0
Impact on the Partnership's net income				1.0	1.0		3.0	3.0
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				$ 9.0	$ 6.0		$ 31.0	$ 23.0
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
ANR Pipeline Company \| Great Lakes \| Firm service between Michigan and Wisconsin \| Expected
Capital and operating costs charged to the pipeline systems and amount payable
Deferred revenue recognized	$ 23.0
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%
Additional acquisition consideration relating to Carty Lateral project			$ 25.0
Former parent, TransCanada subsidiaries \| Transaction between entities under common control \| Bison
Capital and operating costs charged to the pipeline systems and amount payable
Interest acquired (as a percent)											30.00%

FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Millions	Sep. 30, 2015	Mar. 13, 2015	Dec. 31, 2014
Unsecured debt \| 4.65% Senior Notes due 2021
Financial Instruments
Stated interest rate (as a percent)	4.65%		4.65%
Unsecured debt \| 4.375% Senior Notes due 2025
Financial Instruments
Stated interest rate (as a percent)	4.375%	4.375%
Unsecured debt \| 5.09% Senior Notes due 2015
Financial Instruments
Stated interest rate (as a percent)			5.09%
Unsecured debt \| 5.29% Senior Notes due 2020
Financial Instruments
Stated interest rate (as a percent)	5.29%		5.29%
Unsecured debt \| 5.69% Senior Notes due 2035
Financial Instruments
Stated interest rate (as a percent)	5.69%		5.69%
Secured debt \| 3.82% Series D Senior Notes due 2017
Financial Instruments
Stated interest rate (as a percent)	3.82%		3.82%
Carrying Value
Financial Instruments
Debt	$ 1,904		$ 1,695
Carrying Value \| Term loan \| Short-Term Loan Facility due 2015
Financial Instruments
Debt			170
Carrying Value \| Revolving credit facility \| Senior Credit Facility due 2017
Financial Instruments
Debt	190		330
Carrying Value \| Term loan \| 2013 Term Loan Facility due 2018
Financial Instruments
Debt	500		500
Carrying Value \| Term loan \| 2015 Term Loan Facility due 2018
Financial Instruments
Debt	170
Carrying Value \| Unsecured debt \| 4.65% Senior Notes due 2021
Financial Instruments
Debt	350		350
Carrying Value \| Unsecured debt \| 4.375% Senior Notes due 2025
Financial Instruments
Debt	349
Carrying Value \| Unsecured debt \| 5.09% Senior Notes due 2015
Financial Instruments
Debt			75
Carrying Value \| Unsecured debt \| Term Loan Facility due 2019
Financial Instruments
Debt	75
Carrying Value \| Unsecured debt \| 5.29% Senior Notes due 2020
Financial Instruments
Debt	100		100
Carrying Value \| Unsecured debt \| 5.69% Senior Notes due 2035
Financial Instruments
Debt	150		150
Carrying Value \| Secured debt \| 3.82% Series D Senior Notes due 2017
Financial Instruments
Debt	20		20
Fair Value \| Level 2
Financial Instruments
Debt	1,900		1,751
Fair Value \| Level 2 \| Term loan \| Short-Term Loan Facility due 2015
Financial Instruments
Debt			170
Fair Value \| Level 2 \| Revolving credit facility \| Senior Credit Facility due 2017
Financial Instruments
Debt	190		330
Fair Value \| Level 2 \| Term loan \| 2013 Term Loan Facility due 2018
Financial Instruments
Debt	500		500
Fair Value \| Level 2 \| Term loan \| 2015 Term Loan Facility due 2018
Financial Instruments
Debt	170
Fair Value \| Level 2 \| Unsecured debt \| 4.65% Senior Notes due 2021
Financial Instruments
Debt	347		375
Fair Value \| Level 2 \| Unsecured debt \| 4.375% Senior Notes due 2025
Financial Instruments
Debt	330
Fair Value \| Level 2 \| Unsecured debt \| 5.09% Senior Notes due 2015
Financial Instruments
Debt			76
Fair Value \| Level 2 \| Unsecured debt \| Term Loan Facility due 2019
Financial Instruments
Debt	75
Fair Value \| Level 2 \| Unsecured debt \| 5.29% Senior Notes due 2020
Financial Instruments
Debt	109		111
Fair Value \| Level 2 \| Unsecured debt \| 5.69% Senior Notes due 2035
Financial Instruments
Debt	158		168
Fair Value \| Level 2 \| Secured debt \| 3.82% Series D Senior Notes due 2017
Financial Instruments
Debt	$ 21		$ 21

FAIR VALUE MEASUREMENTS (Details 2) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
FAIR VALUE MEASUREMENTS (Details 2) - USD ($) $ in Millions	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Interest rate swaps from September 3, 2013 through July 1, 2018 \| Term loan \| 2013 Term Loan Facility due 2018
Interest rate derivatives
Amount of variable-rate debt hedged	$ 150		$ 150
Weighted average fixed interest rate (as a percent)	2.79%		2.79%
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	$ 2	$ 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	$ 1	2	$ 2
Designated as hedge \| Interest rate swaps \| Recurring fair value measurement \| Level 2
Interest rate derivatives
Fair value of derivatives, gross	3		3		$ 1
Fair value of derivatives, net	$ 3		$ 3		$ 1

ACCOUNTS RECEIVABLE AND OTHER (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
ACCOUNTS RECEIVABLE AND OTHER
Trade accounts receivable, net of allowance of nil	$ 27	$ 30
Accounts receivable from affiliates	1	1
Other	3	4
Accounts receivable and other	31	35
Trade accounts receivable, allowance	$ 0	$ 0

FINANCIAL CHARGES AND OTHER (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
FINANCIAL CHARGES AND OTHER
Interest Expense	$ 15	$ 11	$ 43	$ 35
Amortization of debt issue costs			1	1
Net realized loss related to the interest rate swaps	1	1	2	2
Other Income	(4)	(1)	(5)	(1)
Financial charges and other	$ 12	$ 11	$ 41	$ 37

CONTINGENCIES (Details) $ in Millions	Apr. 01, 2015 USD ($)
Former parent, TransCanada subsidiaries \| Transaction between entities under common control \| GTN \| Partnership interest \| Class B units
Contingencies
Equity issuance	$ 95

SUBSEQUENT EVENTS (Details) - USD ($) $ / shares in Units, $ in Millions	Nov. 02, 2015	Oct. 23, 2015	Oct. 22, 2015	Oct. 09, 2015	Sep. 30, 2015	Mar. 31, 2015
Northern Border
Distributions
Ownership interest (as a percent)					50.00%
Great Lakes
Distributions
Ownership interest (as a percent)					46.45%	46.45%
Subsequent event \| Northern Border \| Revolving credit facility \| Credit Facility renewal and extension maturing October 9, 2020
Distributions
Maximum borrowing capacity				$ 200
Term of the facility				5 years
Subsequent event \| Distribution declared \| Northern Border
Distributions
Partnership distribution		$ 45
Subsequent event \| Distribution declared \| Great Lakes
Distributions
Partnership distribution		$ 7
Subsequent event \| Cash Distribution Paid \| Northern Border
Distributions
Partnership's share of distributions	$ 23
Subsequent event \| Cash Distribution Paid \| Great Lakes
Distributions
Partnership's share of distributions	$ 3
Subsequent event \| Common units
Distributions
Cash distribution (in dollars per unit)			$ 0.89

SUBSEQUENTEVENTS (Details 2) - Subsequent event - Expected - Portland Natural Gas Transmission System - TransCanada - Transaction between entities under common control $ in Millions	Nov. 05, 2015 USD ($)
Acquisition
Interest acquired (as a percent)	49.90%
Purchase price	$ 223
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