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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2019	May 07, 2019
Document and Entity Information
Entity Registrant Name	TC PIPELINES LP
Entity Central Index Key	0001075607
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Small Business	false
Entity Emerging Growth Company	false
Trading Symbol	TCP
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		71,306,396
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1

CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Transmission revenues	$ 113	$ 115
Equity earnings (Note 5)	54	59
Operation and maintenance expenses	(16)	(16)
Property taxes	(7)	(7)
General and administrative	(2)	(1)
Depreciation and amortization	(20)	(24)
Financial charges and other (Note 15)	(22)	(23)
Net income before taxes	100	103
Income taxes		(1)
Net Income	100	102
Net income attributable to non-controlling interests	7	6
Net income attributable to controlling interests	93	96
Net income attributable to controlling interest allocation (Note 9)
General Partner	2	2
Net income attributable to controlling interests	93	96
Common units
Net income attributable to controlling interest allocation (Note 9)
Net income attributable to common units	$ 91	$ 94
Net income per common unit (Note 9) - basic and diluted	$ 1.28	$ 1.32
Weighted average common units outstanding - basic and diluted	71.3	71.2
Common units outstanding, end of period	71.3	71.3

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Net income	$ 100	$ 102
Other comprehensive income
Change in fair value of cash flow hedges (Note 13)	(5)	7
Comprehensive income	95	109
Comprehensive income attributable to non-controlling interests	7	6
Comprehensive income attributable to controlling interests	$ 88	$ 103

- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

+ References

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+ Details

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Current Assets
Cash and cash equivalents	$ 52	$ 33
Accounts receivable and other (Note 14)	41	48
Inventories	9	8
Other	5	8
Total current assets	107	97
Equity investments (Note 5)	1,196	1,196
Property, plant and equipment (Net of $1,128 accumulated depreciation; 2018 - $1,110)	1,522	1,529
Goodwill	71	71
Other assets	3	6
TOTAL ASSETS	2,899	2,899
Current Liabilities
Accounts payable and accrued liabilities	29	36
Accounts payable to affiliates (Note 12)	7	6
Accrued interest	20	12
Current portion of long-term debt (Note 7)	36	36
Total current liabilities	92	90
Long-term debt, net (Note 7)	2,040	2,072
Deferred state income taxes (Note 18)	9	9
Other liabilities	31	29
Total liabilities	2,172	2,200
Partners' Equity
General partner	14	13
Accumulated other comprehensive income (AOCI)	3	8
Controlling interests	619	591
Non-controlling interest	108	108
Total partners' equity	727	699
TOTAL LIABILITIES AND PARTNERS' EQUITY	2,899	2,899
Common units
Partners' Equity
Limited partner	507	462
Class B units
Partners' Equity
Limited partner	$ 95	$ 108

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
CONSOLIDATED BALANCE SHEETS
Accumulated depreciation	$ 1,128	$ 1,110

CONSOLIDATED STATEMENT OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash Generated from Operations
Net income	$ 100	$ 102
Depreciation and amortization	20	24
Amortization of debt issue costs reported as interest expense		1
Equity earnings from equity investments (Note 5)	(54)	(59)
Distributions received from operating activities of equity investments (Note 5)	56	43
Change in operating working capital (Note 11)	13	6
Cash generated from operations	135	117
Investing Activities
Investment in Great Lakes (Note 5)	(5)	(4)
Distribution received from Iroquois as return of investment (Note 5)	2	2
Capital expenditures	(16)	(2)
Customer advances for construction	2
Investing activities	(17)	(4)
Financing Activities
Distributions paid to common units, including the general partner (Note 10)	(47)	(76)
Distributions paid to Class B units (Note 8)	(13)	(15)
Distributions paid to non-controlling interests	(7)	(1)
Common unit issuance, net		40
Long-term debt issued, net of discount (Note 7)	18	75
Long-term debt repaid (Note 7)	(50)	(101)
Financing activities	(99)	(78)
Increase in cash and cash equivalents	19	35
Cash and cash equivalents, beginning of period	33	33
Cash and cash equivalents, end of period	$ 52	$ 68

CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY - 3 months ended Mar. 31, 2019 - USD ($)
shares in Millions, $ in Millions

Limited Partners

Common units

Limited Partners

Class B units

General Partner

Accumulated Other Comprehensive Income

^[1]

Non-controlling interest

Total

Partners' Equity at beginning of period at Dec. 31, 2018

$ 462

$ 108

$ 13

$ 8

$ 108

$ 699

Partners' Equity at beginning of period (in units) at Dec. 31, 2018

71.3

1.9

Increase (Decrease) in Partners' Equity

Net income

$ 91

100

Other comprehensive income

(5)

Distributions (Note 10)

(46)

$ (13)

(1)

(7)

(67)

Partners' Equity at end of period at Mar. 31, 2019

$ 507

$ 95

$ 14

$ 3

$ 108

$ 727

Partners' Equity at end of period (in units) at Mar. 31, 2019

71.3

1.9

[1]

Gain (Losses) related to cash flow hedges reported in AOCI 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.

- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

+ References

+ Details

CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY (Parenthetical) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY
Gain (Losses) related to cash flow hedges in AOCI expected to be reclassified to Net income in the next 12 months	$ 1

ORGANIZATION	3 Months Ended
ORGANIZATION	Mar. 31, 2019
ORGANIZATION
ORGANIZATION	NOTE 1 ORGANIZATION 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 now known as TC Energy Corporation (TC Energy Corporation together with its subsidiaries collectively referred to herein as TC Energy), to acquire, own and participate in the management of energy infrastructure assets in North America. The Partnership owns its pipeline assets through an intermediate general partnership, TC PipeLines Intermediate GP, LLC and three intermediate limited partnerships (ILPs), TC GL Intermediate Limited Partnership, TC PipeLines Intermediate Limited Partnership and TC Tuscarora Intermediate Limited Partnership.

SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
SIGNIFICANT ACCOUNTING POLICIES	Mar. 31, 2019
SIGNIFICANT ACCOUNTING POLICIES
SIGNIFICANT ACCOUNTING POLICIES	NOTE 2 SIGNIFICANT ACCOUNTING POLICIES The accompanying consolidated 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 months ended March 31, 2019 and 2018 are not necessarily indicative of the results that may be expected for the full fiscal year. The accompanying consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto for the year ended December 31, 2018 included in our Annual Report on Form 10-K. That report contains a more comprehensive summary of the Partnership’s significant accounting policies. In the opinion of management, the accompanying consolidated financial statements contain all of the appropriate adjustments, which are normally recurring adjustments unless otherwise noted, and considered necessary to present fairly the financial position of the Partnership, the results of operations and cash flows for the respective periods. Our significant accounting policies are consistent with those disclosed in our Annual Report on Form 10-K for the year ended December 31, 2018, except as described in Note 3, Accounting Pronouncements. Basis of Presentation The Partnership consolidates its interests in entities over which it is able to exercise control. To the extent there are interests owned by other parties, these interests are included as non-controlling interests. The Partnership uses the equity method of accounting for its investments in entities over which it is able to exercise significant influence. Acquisitions by the Partnership from TC Energy are considered common control transactions. If businesses are acquired from TC Energy that will be consolidated by the Partnership, the historical consolidated financial statements are required to be recast, except net income per common unit, to include the acquired entities for all periods presented. If the Partnership acquires an asset or an investment from TC Energy, which will be accounted for by the equity method, the financial information is not required to be recast and the transaction is accounted for prospectively from the date of the acquisition. U.S. federal and certain state income taxes are the responsibility of the partners and are not reflected in these consolidated financial statements. The tax effect of the Partnership's activities accrues to its partners. The Partnership's taxable income or loss, which may vary substantially from the net income or loss reported in the consolidated statement of operations, is includable in the U.S. federal income tax returns of each partner. In instances where the Partnership's consolidated entities are subject to state income taxes, the asset-liability method is used to account for taxes. This method requires the recognition of deferred tax assets and liabilities for future tax consequences attributable to the differences between the financial statement carrying amount of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are classified as non-current on our consolidated balance sheet. 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, if any, 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

3 Months Ended

Mar. 31, 2019

ACCOUNTING PRONOUNCEMENTS

ACCOUNTING PRONOUNCEMENTS

NOTE 3 ACCOUNTING PRONOUNCEMENTS

Changes in Accounting Policies effective January 1, 2019

Leases

In February 2016, the Financial Accounting Standards Board (FASB) issued new guidance on the accounting for leases. The new guidance amends the definition of a lease such that, in order for an arrangement to qualify as a lease, the lessee is required to have both (1) the right to obtain substantially all of the economic benefits from the use of the asset and (2) the right to direct the use of the asset. The new guidance also establishes a right-of-use (ROU) model that requires a lessee to recognize a ROU asset and corresponding lease liability on the consolidated balance sheet for all leases with a term longer than twelve months. Leases will be classified as finance or operating, with classification affecting the pattern of expense recognition in the consolidated statements of income. The new guidance does not make extensive changes to previous lessor accounting.

Under the new guidance, the Partnership determines if an arrangement is a lease at inception. Operating leases are recognized as ROU assets and included in Property, plant and equipment while corresponding liabilities are included in “Accounts payable and other”, and “Other long-term liabilities” on the consolidated balance sheet.

Operating lease ROU assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. As the Partnership's leases do not provide an implicit rate, the Partnership uses an incremental borrowing rate that approximates its borrowing cost based on the information available at commencement date in determining the present value of future payments. The operating lease ROU asset also includes any lease payments made and initial direct costs incurred and excludes lease incentives. Lease terms may include options to extend or terminate the lease when it is reasonably certain that the Partnership will exercise that option. Operating lease expense is recognized on a straight-line basis over the lease term and included in “Operation and maintenance expenses” in the consolidated statements of income.

The new guidance was effective January 1, 2019 and was applied using optional transition relief which allowed entities to initially apply the new lease standard at adoption and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. This transition option allowed us to not apply the new guidance, including disclosure requirements, to the comparative periods presented.

We elected available practical expedients and exemptions upon adoption which allowed us:

not to reassess prior conclusions on existing leases regarding lease identification, lease classification and initial direct costs under the new standard

to carry forward the historical lease classification and our accounting treatment for land easements on existing agreements

to not recognize ROU assets or lease liabilities for leases that qualify for the short-term lease recognition exemption

to not separate lease and non-lease components for all leases for which we are the lessee

to use hindsight in determining the lease term and assessing ROU assets for impairment.

In the application of the new guidance, assumptions and judgements are used to determine the following:

whether a contract contains a lease and the duration of the lease term including exercising lease renewal options. The lease term for all of the Partnership’s leases includes the non-cancellable period of the lease plus any additional periods covered by either the Partnership’s option to extend (or not to terminate) the lease that the Partnership is reasonably certain to exercise, or an option to extend (or not to terminate) the lease controlled by the lessor ; and

the discount rate for the lease.

The standard did not impact our previously reported results and did not have material impact on the Partnership's consolidated balance sheet, consolidated statements of income or consolidated statement of cash flows at the date of adoption.

The most significant change as a result of the adoption was the recognition of ROU assets and lease liabilities for operating leases which was approximately $0.6 million at January 1, 2019 and $0.5 million at March 31, 2019. For the three months ended March 31, 2019, the Partnership’s operating lease cost was not material to the Partnership’s consolidated results. The weighted average remaining term and discount rate of the Partnership’s operating leases was approximately 2.63 years and 3.57 percent, respectively.

Fair Value Measurement

In August 2018, the FASB issued new guidance that amends certain disclosure requirements for the fair value measurements as part of its disclosure framework project. This new guidance is effective January 1, 2020, however, early adoption of certain or all requirements is permitted. The Partnership elected to adopt this guidance effective first quarter 2019. The guidance was applied retrospectively and did not have a material effect on the Partnership’s consolidated financial statements.

Future accounting changes

Measurement of credit losses on financial instruments

In June 2016, the FASB issued new guidance that significantly changes how entities measure credit losses for most financial assets and certain other financial instruments that are not measured at fair value through net income (loss). The new guidance amends the impairment model of financial instruments basing it on expected losses rather than incurred losses. These expected credit losses will be recognized as an allowance rather than as a direct write down of the amortized cost basis. The new guidance is effective January 1, 2020 and will be applied using a modified retrospective approach. We are currently evaluating the impact of the adoption of this guidance and have not yet determined the effect on our consolidated financial statements.

Consolidation

In October 2018, the FASB issued new guidance for determining whether fees paid to decision makers and service providers are variable interests for indirect interests held through related parties under common control. This new guidance is effective January 1, 2020, and will be applied on a retrospective basis, however early adoption is permitted. The Partnership is currently evaluating the timing and impact of adoption of this guidance and has not yet determined the effect on its consolidated financial statements.

REGULATORY	3 Months Ended
REGULATORY	Mar. 31, 2019
REGULATORY
REGULATORY	NOTE 4 REGULATORY Iroquois, Tuscarora , and Northern Border took the actions listed below to conclude the issues impacting their pipelines as contemplated by the 2017 Tax Act and certain FERC actions that began in March of 2018, namely FERC’s Revised Policy Statement on Treatment of Income Taxes (Revised Policy Statement) and a Final Rule that established a schedule by which interstate pipelines must either (i) file a new uncontested rate settlement or (ii) file a one-time report, called FERC Form No. 501-G, that quantified the rate impact of the 2017 Tax Act on FERC-regulated pipelines and the impact of the Revised Policy Statement on pipelines held by an MLP (collectively “2018 FERC Actions”). Iroquois On February 28, 2019, Iroquois filed an uncontested settlement with FERC to address the issues contemplated by the 2017 Tax Act and 2018 FERC Actions via an amendment to its prior 2016 settlement (2019 Iroquois Settlement). Among the terms of the 2019 Iroquois Settlement, Iroquois agreed to reduce its existing maximum system rates by 6.5 percent to be implemented in two phases, (i) effective March 1, 2019, a 3.25 percent rate reduction and (ii) effective April 1, 2020, an additional 3.25 percent rate reduction, which is the remaining one-half of the total 6.5 percent rate reduction from the 2016 settlement rates. The 2019 Iroquois Settlement, which was approved by FERC on May 2, 2019, preserved the 2016 settlement moratorium on further rate changes until September 1, 2020. Unless superseded by a subsequent rate case or settlement, Iroquois will be required to have new rates in effect on March 1, 2023. Tuscarora On March 15, 2019, Tuscarora filed an uncontested settlement with FERC to address the issues contemplated by the 2017 Tax Act and 2018 FERC Actions via an amendment to its prior 2016 settlement (2019 Tuscarora Settlement). Among the terms of the 2019 Tuscarora Settlement, Tuscarora agreed to reduce its existing maximum system rates by 1.7 percent effective February 1, 2019 through to July 31, 2019. The existing maximum rates will decrease by an additional 10.8 percent for the period August 1, 2019 through the term of the settlement. Tuscarora is required to have new rates in effect on February 1, 2023. Tuscarora and its customers also agreed on a moratorium on further rate changes until January 31, 2023. The 2019 Tuscarora Settlement, which was approved by FERC on May 2, 2019, will also reflect an elimination of the tax allowance previously recovered in rates along with accumulated deferred income taxes (ADIT) for rate-making purposes. Northern Border On April 4, 2019, Northern Border filed a petition for approval with FERC to amend the settlement agreement reached with its customers in 2017. Unless superseded by a subsequent rate case or settlement, effective January 1, 2020, the additional 2 percent rate reduction implemented on February 1, 2019 will be extended to July 1, 2024 as part of the amended settlement agreement. The amendment is pending approval from FERC.

EQUITY INVESTMENTS

3 Months Ended

Mar. 31, 2019

EQUITY INVESTMENTS

EQUITY INVESTMENTS

NOTE 5 EQUITY INVESTMENTS

The Partnership has equity interests in Northern Border, Great Lakes and Iroquois. The pipeline systems owned by these entities are regulated by FERC. The pipeline systems of Northern Border and Great Lakes are operated by subsidiaries of TC Energy. The Iroquois pipeline system is operated by Iroquois Pipeline Operating Company, a wholly owned subsidiary of Iroquois. The Partnership uses the equity method of accounting for its interests in its equity investees. The Partnership’s equity investments are held through our ILPs that are considered to be variable interest entities (VIEs) (Refer to Note 16).


	Ownership		Equity Earnings		Equity Investments
	Interest at		Three months
(unaudited)	March 31,		Ended March 31,		March 31,	December 31,
(millions of dollars)	2019		2019	2018	2019	2018

Northern Border	50	%	21	17	489	497
Great Lakes	46.45	%	20	24	498	489
Iroquois	49.34	%	13	18	209	210
			54	59	1,196	1,196

Distributions from Equity Investments

Distributions received from equity investments in the three months ended March 31, 2019 were $58 million (March 31, 2018 – $45 million) of which, $2 million (March 31, 2018 - $2 million) was considered a return of capital and is included in “Investing Activities” in the Partnership’s consolidated statement of cash flows. The return of capital was related to our investment in Iroquois (see further discussion below).

Northern Border

The Partnership did not have undistributed earnings from Northern Border for the three months ended March 31, 2019 and 2018.

The summarized financial information provided to us by Northern Border is as follows:


(unaudited)
(millions of dollars)	March 31, 2019	December 31, 2018

ASSETS
Cash and cash equivalents	14	10
Other current assets	38	36
Property, plant and equipment, net	1,023	1,037
Other assets	13	13
	1,088	1,096

LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	41	34
Deferred credits and other	35	35
Long-term debt, net (a)	264	264
Partners’ equity
Partners’ capital	749	764
Accumulated other comprehensive loss	(1)	(1)
	1,088	1,096


	Three months ended
(unaudited)	March 31,
(millions of dollars)	2019	2018

Transmission revenues	81	72
Operating expenses	(20)	(19)
Depreciation	(15)	(15)
Financial charges and other	(4)	(4)
Net income	42	34

(a)No current maturities as of March 31, 2019 and December 31, 2018. At March 31, 2019, Northern Border is in compliance with all its financial covenants.

Great Lakes

The Partnership made an equity contribution to Great Lakes of $5 million in the first quarter of 2019 (March 31, 2018 - $4 million). This amount represents the Partnership’s 46.45 percent share of an $11 million cash call from Great Lakes to make a scheduled debt repayment.

The Partnership did not have undistributed earnings from Great Lakes for the three months ended March 31, 2019 and 2018.

The summarized financial information provided to us by Great Lakes is as follows:


(unaudited)
(millions of dollars)	March 31, 2019	December 31, 2018

ASSETS
Current assets	86	75
Property, plant and equipment, net	685	689
	771	764

LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	25	26
Net long-term debt, including current maturities (a)	229	240
Other long-term liabilities	4	4
Partners' equity	513	494
	771	764


	Three months ended
(unaudited)	March 31,
(millions of dollars)	2019	2018

Transmission revenues	72	81
Operating expenses	(16)	(17)
Depreciation	(8)	(8)
Financial charges and other	(4)	(4)
Net income	44	52

(a) Includes current maturities of $21 million as of March 31, 2019 and as of December 31, 2018. At March 31, 2019, Great Lakes is in compliance with all its financial covenants.

Iroquois

During the three months ended March 31, 2019, the Partnership received distributions from Iroquois amounting to $14 million (March 31, 2018 - $14 million) which includes the Partnership’s 49.34 percent share of the Iroquois unrestricted cash distribution amounting to approximately $2 million (March 31, 2018 - $2 million). The unrestricted cash did not represent a distribution of Iroquois’ cash from operations during the period and therefore it was reported as distributions received as return of investment in the Partnership’s consolidated statement of cash flows.

Iroquois declared its first quarter 2019 distribution of $28 million on April 24, 2019, of which the Partnership received its 49.34 percent share or $14 million on May 1, 2019. The distribution includes our 49.34 percent share of the Iroquois unrestricted cash distribution amounting to approximately $2 million. The Partnership did not have undistributed earnings from Iroquois for the three months ended March 31, 2019 and 2018.

The summarized financial information provided to us by Iroquois is as follows:


(unaudited)
(millions of dollars)	March 31, 2019	December 31, 2018

ASSETS
Cash and cash equivalents	84	80
Other current assets	30	32
Property, plant and equipment, net	576	581
Other assets	16	8
	706	701

LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	19	19
Long-term debt, net (a)	325	325
Other non-current liabilities	20	14
Partners' equity	342	343
	706	701


	Three months ended
(unaudited)	March 31,
(millions of dollars)	2019	2018

Transmission revenues	52	60
Operating expenses	(15)	(14)
Depreciation	(7)	(7)
Financial charges and other	(3)	(4)
Net income	27	35

^(a)

Includes current maturities of $146 million as of March 31, 2019 and as of December 31, 2018. At March 31, 2019, Iroquois is in compliance with all its financial covenants.

REVENUES	3 Months Ended
REVENUES	Mar. 31, 2019
REVENUES
REVENUES	NOTE 6 REVENUES Disaggregation of Revenues For the three months ended March 31, 2019 and March 31, 2018, effectively all of the Partnership’s revenues were from capacity arrangements and transportation contracts with customers as discussed in more detail below. Capacity Arrangements and Transportation Contracts The Partnership’s performance obligations in its contracts with customers consist primarily of capacity arrangements and natural gas transportation contracts. The Partnership’s revenues are generated from contractual arrangements for committed capacity and from transportation of natural gas which are treated as a bundled performance obligation. Revenues earned from firm contracted capacity arrangements are recognized ratably over the term of the contract regardless of the amount of natural gas that is transported. Transportation revenues for interruptible or volumetric-based services are recognized when the service is performed. The Partnership has elected to utilize the practical expedient of recognizing revenue as invoiced. The Partnership's pipeline systems are subject to FERC regulations and, as a result, a portion of revenues collected may be subject to refund if invoiced during an interim period when a rate proceeding is ongoing. Allowances for these potential refunds are recognized using management's best estimate based on the facts and circumstances of the proceeding. Any allowances that are recognized during the proceeding process are refunded or retained, as applicable, at the time a regulatory decision becomes final. As of March 31, 2019, the Partnership does not have any outstanding refund obligations related to any rate proceedings. Revenues are invoiced and paid on a monthly basis. The Partnership’s pipeline systems do not take ownership of the natural gas that is transported for customers. Revenues from contracts with customers are recognized net of any taxes collected from customers, which are subsequently remitted to governmental authorities. Contract Balances All of the Partnership’s contract balances pertain to receivables from contracts with customers amounting to $35 million at March 31, 2019 (December 31, 2018 - $44 million) and are recorded as Trade accounts receivable and reported as “Accounts receivable and other” in the Partnership’s consolidated balance sheet (Refer to Note 14). Additionally, our accounts receivable represents the Partnership’s unconditional right to consideration for services completed which includes billed and unbilled accounts. Future revenue from remaining performance obligations When the right to invoice practical expedient is applied, the guidance does not require disclosure of information related to future revenue from remaining performance obligations; therefore, no additional disclosure is required. Additionally, in the application of the right to invoice practical expedient, the Partnership’s revenues from regulated capacity arrangements are recognized based on rates specified in the contract. Therefore, the amount invoiced, which includes the capacity contracted and variable volume of natural gas transported, corresponds directly to the value the customer received. These revenues are recognized on a monthly basis once the Partnership’s performance obligation to provide capacity has been satisfied.

DEBT AND CREDIT FACILITIES

3 Months Ended

Mar. 31, 2019

DEBT AND CREDIT FACILITIES

DEBT AND CREDIT FACILITIES

NOTE 7 DEBT AND CREDIT FACILITIES


		Weighted Average				Weighted Average
		Interest Rate for the				Interest Rate for the
(unaudited)		Three Months Ended			December 31,	Year Ended
(millions of dollars)	March 31, 2019	March 31, 2019			2018	December 31, 2018
TC PipeLines, LP
Senior Credit Facility due 2021	—	3.61	%		40	3.14	%
2013 Term Loan Facility due 2022	500	3.73	%		500	3.23	%
4.65% Unsecured Senior Notes due 2021	350	4.65	%	(a)	350	4.65	%	(a)
4.375% Unsecured Senior Notes due 2025	350	4.375	%	(a)	350	4.375	%	(a)
3.90 % Unsecured Senior Notes due 2027	500	3.90	%	(a)	500	3.90	%	(a)
GTN
5.29% Unsecured Senior Notes due 2020	100	5.29	%	(a)	100	5.29	%	(a)
5.69% Unsecured Senior Notes due 2035	150	5.69	%	(a)	150	5.69	%	(a)
Unsecured Term Loan Facility due 2019	35	3.45	%		35	2.93	%
PNGTS
Revolving Credit Facility due 2023	27	3.75	%		19	3.55	%
Tuscarora
Unsecured Term Loan due 2020	24	3.63	%		24	3.10	%
North Baja
Unsecured Term Loan due 2021	50	3.56	%		50	3.54	%
	2,086				2,118
Less: unamortized debt issuance costs and debt discount	10				10
Less: current portion	36				36
	2,040				2,072

(a) Fixed interest rate

TC PipeLines, LP

The Partnership’s Senior Credit Facility consists of a $500 million senior revolving credit facility with a banking syndicate, maturing November 10, 2021. During the three months ended March 31, 2019, the Partnership repaid all amounts outstanding under its Senior Credit Facility and there was no outstanding balance at March 31, 2019 (December 31, 2018 - $40 million).

The LIBOR-based interest rate on the Senior Credit Facility was 3.77 percent at December 31, 2018.

As of March 31, 2019, the variable interest rate exposure related to the 2013 Term Loan Facility was hedged using interest rate swaps at an average rate of 3.26 percent (December 31, 2018 – 3.26 percent). Prior to hedging activities, the LIBOR-based interest rate on the 2013 Term Loan Facility was 3.74 percent at March 31, 2019 (December 31, 2018 – 3.60 percent).

The Senior Credit Facility and the 2013 Term Loan Facility require the Partnership to maintain a certain leverage ratio (debt to adjusted cash flow [net income plus cash distributions received, extraordinary losses, interest expense, expense for taxes paid or accrued, and depreciation and amortization expense less equity earnings and extraordinary gains]) no greater than 5.00 to 1.00 for each fiscal quarter, except for the fiscal quarter and the two following fiscal quarters in which one or more acquisitions has been executed, in which case the leverage ratio is to be no greater than 5.50 to 1.00. The leverage ratio was 3.03 to 1.00 as of March 31, 2019.

GTN

GTN’s Unsecured Senior Notes, along with GTN’s Unsecured Term Loan Facility contain a covenant that limits total debt to no greater than 70 percent of GTN’s total capitalization. GTN’s total debt to total capitalization ratio at March 31, 2019 was 42.5 percent.

The LIBOR-based interest rate on GTN’s Unsecured Term Loan Facility was 3.44 percent at March 31, 2019 (December 31, 2018 – 3.30 percent).

PNGTS

PNGTS’ Revolving Credit Facility requires PNGTS to maintain a leverage ratio not greater than 5.00 to 1.00. The leverage ratio was 0.47 to 1.00 as of March 31, 2019.

The LIBOR-based interest rate on PNGTS’ Revolving Credit Facility was 3.74 percent at March 31, 2019 (December 31, 2018 – 3.60 percent).

Tuscarora

Tuscarora’s Unsecured Term Loan contains a covenant that requires Tuscarora to maintain a debt service coverage ratio (cash available from operations divided by a sum of interest expense and principal payments) of greater than or equal to 3.00 to 1.00. As of March 31, 2019, the ratio was 10.14 to 1.00.

The LIBOR-based interest rate on the Tuscarora’s Unsecured Term Loan Facility was 3.61 percent at March 31, 2019 (December 31, 2018 – 3.47 percent).

North Baja

North Baja’s Term Loan Facility contains a covenant that limits total debt to no greater than 70 percent of North Baja’s total capitalization. North Baja’s total debt to total capitalization ratio at March 31, 2019 was 38.11 percent.

The LIBOR-based interest rate on North Baja’s Term Loan Facility was 3.56 percent at March 31, 2019 (December 31, 2018 - 3.54 percent).

Partnership (TC PipeLines, LP and its subsidiaries)

At March 31, 2019, 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 Fourth 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)		Principal payments
2019		36
2020		123
2021		400
2022		500
2023		27
Thereafter		1,000
		2,086

PARTNERS' EQUITY	3 Months Ended
PARTNERS' EQUITY	Mar. 31, 2019
PARTNERS' EQUITY
PARTNERS' EQUITY	NOTE 8 PARTNERS’ EQUITY ATM equity issuance program (ATM program) During the three months ended March 31, 2019, no common units were issued under this program. Class B units issued to TC Energy The Class B units entitle TC Energy to an annual distribution based on 30 percent of GTN’s annual distributions as follows: (i) 100 percent of distributions above $20 million for the year ending December 31, 2019; (ii) 43.75 percent of distributions above $20 million for the year ending December 31, 2020; and (iii) 25 percent of distributions above $20 million thereafter (Class B Distribution). Additionally, the Class B Distribution will be further reduced by 35 percent, which is equivalent to the percentage by which distributions payable to the common units were reduced in 2018 (Class B Reduction). The Class B Reduction was implemented during the first quarter of 2018 following the Partnership’s common unit distribution reduction of 35 percent. The Class B Reduction will continue to apply for any particular calendar year until distributions payable in respect of common units for such calendar year equal or exceed $3.94 per common unit. For the year ended December 31, 2019, the Class B units’ equity account will be increased by the Class B Distribution, less the Class B Reduction, until such amount is declared for distribution and paid in the first quarter of 2020. During the three months ended March 31, 2019, the Class B threshold was not exceeded. For the year ended December 31, 2018, the Class B distribution was $13 million and was declared and paid in the first quarter of 2019.

NET INCOME PER COMMON UNIT

3 Months Ended

Mar. 31, 2019

NET INCOME PER COMMON UNIT

NET INCOME PER COMMON UNIT

NOTE 9 NET 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 amount allocable to the General Partner equals an amount based upon the General Partner’s two percent general partner interest, plus an amount equal to incentive distributions. Incentive distributions are paid to the General Partner if quarterly cash distributions on the common units exceed levels specified in the Partnership Agreement.

The amount allocable to the Class B units in 2019 equals 30 percent of GTN’s distributable cash flow during the year ended December 31, 2019 less $20 million and is further reduced by the estimated Class B Reduction for 2019 (December 31, 2018 – $20 million less Class B Reduction). During the three months ended March 31, 2019 and 2018, no amounts were allocated to the Class B units as the annual threshold was not exceeded.

Net income per common unit was determined as follows:



(unaudited)	Three months ended March 31,
(millions of dollars, except per common unit amounts)	2019		2018

Net income attributable to controlling interests		93		96
Net income attributable to the General Partner		(2)		(2)
Net income attributable to common units		91		94
Weighted average common units outstanding (millions) – basic and diluted		71.3		71.2
Net income per common unit – basic and diluted	$	1.28	$	1.32

CASH DISTRIBUTIONS PAID TO COMMON UNITS	3 Months Ended
CASH DISTRIBUTIONS PAID TO COMMON UNITS	Mar. 31, 2019
CASH DISTRIBUTIONS PAID TO COMMON UNITS
CASH DISTRIBUTIONS PAID TO COMMON UNITS	NOTE 10 CASH DISTRIBUTIONS PAID TO COMMON UNITS During the three months ended March 31, 2019, the Partnership distributed $0.65 per common unit (March 31, 2018 – $1.00 per common unit) for a total of $47 million (March 31, 2018 - $76 million). The distribution paid to our General Partner during the three months ended March 31, 2019 for its two percent general partner interest was $1 million (March 31, 2018 - $2 million). The General Partner did not receive any distributions in respect of its IDRs during the three months ended March 31, 2019 (March 31, 2018 - $3 million).

CHANGE IN OPERATING WORKING CAPITAL

3 Months Ended

Mar. 31, 2019

CHANGE IN OPERATING WORKING CAPITAL

CHANGE IN OPERATING WORKING CAPITAL

NOTE 11 CHANGE IN OPERATING WORKING CAPITAL


(unaudited)	Three months ended March 31,
(millions of dollars)	2019	2018

Change in accounts receivable and other	7	—
Change in inventories	(1)	—
Change in other current assets	2	(3)
Change in accounts payable and accrued liabilities	(4)	—
Change in accounts payable to affiliates	1	—
Change in accrued interest	8	9
Change in operating working capital	13	6

RELATED PARTY TRANSACTIONS

3 Months Ended

Mar. 31, 2019

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS

NOTE 12 RELATED 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 conduct 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. For both the three months ended March 31, 2019 and 2018, total costs charged to the Partnership by the General Partner were $1 million.

As operator of our pipelines, except Iroquois, TC Energy’s subsidiaries provide capital and operating services to our pipeline systems. TC Energy’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. Iroquois does not receive any capital and operating services from TC Energy (Refer to Note 5).

Capital and operating costs charged to our pipeline systems, except for Iroquois, for the three months ended March 31, 2019 and 2018 by TC Energy’s subsidiaries and amounts payable to TC Energy’s subsidiaries at March 31, 2019 and December 31, 2018 are summarized in the following tables:


	Three months ended
(unaudited)	March 31,
(millions of dollars)	2019	2018

Capital and operating costs charged by TC Energy’s subsidiaries to:
Great Lakes (a)	11	9
Northern Border (a)	9	9
GTN	10	8
Bison	1	2
North Baja	1	1
Tuscarora	1	1
PNGTS (a)	2	2
Impact on the Partnership’s net income:
Great Lakes	5	4
Northern Border	4	4
GTN	8	8
Bison	1	2
North Baja	1	1
Tuscarora	1	1
PNGTS	1	1


(unaudited)
(millions of dollars)	March 31, 2019	December 31, 2018

Net amounts payable to TC Energy’s subsidiaries are as follows:
Great Lakes (a)	5	3
Northern Border (a)	4	3
GTN	4	4
Bison	—	1
North Baja	1	—
Tuscarora	—	1
PNGTS (a)	1	1

^(a)

Represents 100 percent of the costs.

Great Lakes

Great Lakes earns significant transportation revenues from TC Energy and its affiliates, some of which are provided at discounted rates and some at maximum recourse rates. For the three months ended March 31, 2019, Great Lakes earned 73 percent of transportation revenues from TC Energy and its affiliates (March 31, 2018 – 68 percent).

At March 31, 2019, $18 million was included in Great Lakes’ receivables with regard to the transportation contracts with TC Energy and its affiliates (December 31, 2018 – $18 million).

During the second quarter of 2018, Great Lakes reached an agreement on the terms of new long-term transportation capacity contracts with its affiliate, ANR Pipeline Company. The contracts are for a term of 15 years from November 2021 to October 31, 2036 with a total contract value of approximately $1.3 billion. The contracts contain reduction options (i) at any time on or before April 1, 2019 for any reason and (ii) any time before April 2021, if TC Energy is not able to secure the required regulatory approval related to anticipated expansion projects. During the first quarter of 2019, Great Lakes reached an agreement to amend volume reduction “for any reason” option by extending the period “on or before” April 1, 2019 to “on or before” April 1, 2020. All the other terms remained the same.

PNGTS

PNGTS earns transportation revenues from TC Energy and its affiliates. For the three months ended March 31, 2019, PNGTS earned approximately nil of its transportation revenues from TC Energy and its affiliates (March 31, 2018 – $1 million).

At March 31, 2019, PNGTS had nil outstanding receivables with regard to the transportation contracts with TC Energy and its affiliates (December 31, 2018 – nil).

In connection with anticipated future commercial opportunities, PNGTS has entered into an arrangement with its affiliates regarding the construction of certain facilities on their systems that will be required to fulfill future contracts on the PNGTS system. In the event the anticipated developments do not proceed, PNGTS will be required to reimburse its affiliates for any costs incurred related to the development of these facilities. At March 31, 2019, the total costs incurred by these affiliates was approximately $71 million.

FAIR VALUE MEASUREMENTS

3 Months Ended

Mar. 31, 2019

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS

NOTE 13 FAIR VALUE MEASUREMENTS

(a) Fair Value Hierarchy

Under Accounting Standards Codification (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 Partnership has classified the fair value of natural gas imbalances as a Level 2 of the fair value hierarchy for fair value disclosure purposes, as the valuation approach includes quoted prices in the market index and observable volumes for the imbalance.

Long-term debt is recorded at amortized cost and classified as Level 2 of the fair value hierarchy for fair value disclosure purposes. Interest rate derivative assets and liabilities are classified as Level 2 for all periods presented where the fair value is determined by using valuation techniques that refer to observable market data or estimated market prices. The estimated fair value of the Partnership’s debt as at March 31, 2019 and December 31, 2018 was $2,119 million and $2,101 million, respectively.

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 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 Partnership’s interest rate swaps mature on October 2, 2022 and 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 fixed weighted average interest rate on these instruments is 3.26 percent.

At March 31, 2019, the fair value of the interest rate swaps accounted for as cash flow hedges was an asset of $3 million (both on a gross and net basis) (December 31, 2018 - asset of $8 million).

The change in fair value of interest rate derivative instruments recognized in other comprehensive income was a loss of $5 million for the three months ended March 31, 2019 (March 31, 2018 – gain of $7 million). For the three months ended March 31, 2019, the net realized gain related to the interest rate swaps was $1 million, and was included in “financial charges and other” (March 31, 2018 - gain of $1 million) (Refer to Note 15).

The Partnership has no master netting agreements; however, it has derivative contracts containing provisions with rights of offset. The Partnership has elected to present the fair value of derivative instruments with the right to offset on a gross basis in the consolidated 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 March 31, 2019 and December 31, 2018.

ACCOUNTS RECEIVABLE AND OTHER

3 Months Ended

Mar. 31, 2019

ACCOUNTS RECEIVABLE AND OTHER

ACCOUNTS RECEIVABLE AND OTHER

NOTE 14 ACCOUNTS RECEIVABLE AN.D OTHER


(unaudited)
(millions of dollars)	March 31, 2019	December 31, 2018

Trade accounts receivable, net of allowance of nil	35	44
Imbalance receivable from affiliates	4	2
Other	2	2
	41	48

FINANCIAL CHARGES AND OTHER

3 Months Ended

Mar. 31, 2019

FINANCIAL CHARGES AND OTHER

FINANCIAL CHARGES AND OTHER

NOTE 15 FINANCIAL CHARGES AND OTHER


	Three months ended
(unaudited)	March 31,
(millions of dollars)	2019	2018

Interest expense (a)	23	24
Net realized gain related to the interest rate swaps	(1)	(1)
	22	23

^(a)

Includes amortization of debt issuance costs and discount costs.

VARIABLE INTEREST ENTITIES

3 Months Ended

Mar. 31, 2019

VARIABLE INTEREST ENTITIES

VARIABLE INTEREST ENTITIES

NOTE 16 VARIABLE INTEREST ENTITIES

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

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

Consolidated VIEs

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

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


(unaudited)
(millions of dollars)	March 31, 2019	December 31, 2018

ASSETS (LIABILITIES) (a)
Cash and cash equivalents	25	16
Accounts receivable and other	37	39
Inventories	9	8
Other current assets	5	6
Equity investments	1,196	1,196
Property, plant and equipment, net	1,237	1,240
Other assets	1	1
Accounts payable and accrued liabilities	(26)	(33)
Accounts payable to affiliates, net	(38)	(40)
Accrued interest	(5)	(2)
Current portion of long-term debt	(36)	(36)
Long-term debt	(349)	(341)
Other liabilities	(28)	(27)
Deferred state income tax	(9)	(9)

^(a)

Bison, an asset held through our consolidated VIEs, is excluded at March 31, 2019 and at December 31, 2018 as the assets of this entity can be used for purposes other than the settlement of the VIE’s obligations.

SUBSEQUENT EVENTS	3 Months Ended
SUBSEQUENT EVENTS	Mar. 31, 2019
SUBSEQUENT EVENTS
SUBSEQUENT EVENTS	NOTE 17 SUBSEQUENT EVENTS Management of the Partnership has reviewed subsequent events through May 8, 2019, the date the consolidated 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 April 23, 2019, the board of directors of the General Partner declared the Partnership’s first quarter 2019 cash distribution in the amount of $0.65 per common unit payable on May 13, 2019 to unitholders of record as of May 3, 2019. The declared distribution totaled $47 million and is payable in the following manner: $46 million to common unitholders (including $4 million to the General Partner as a holder of 5,797,106 common units and $7 million to another subsidiary of TC Energy as holder of 11,287,725 common units) and $1 million to the General Partner for its two percent general partner interest. The General Partner did not receive any distributions in respect of its IDRs for the first quarter 2019. Northern Border declared its March 2019 distribution of $15 million on April 9, 2019, of which the Partnership received its 50 percent share or $7 million on April 30, 2019. Great Lakes declared its first quarter 2019 distribution of $49 million on April 16, 2019, of which the Partnership received its 46.45 percent share or $23 million on May 1, 2019. Iroquois declared its first quarter 2019 distribution of $28 million on April 24, 2019, of which the Partnership received its 49.34 percent share or $14 million on May 1, 2019. The $14 million includes our proportionate share of Iroquois’ unrestricted cash amounting to $2 million (refer to Note 5). PNGTS declared its first quarter 2019 distribution of $19 million on April 9, 2019, of which $7 million was paid to its non-controlling interest owner on April 30, 2019.

SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
SIGNIFICANT ACCOUNTING POLICIES (Policies)	Mar. 31, 2019
SIGNIFICANT ACCOUNTING POLICIES
Basis of Presentation - Consolidation and equity method of accounting	Basis of Presentation The Partnership consolidates its interests in entities over which it is able to exercise control. To the extent there are interests owned by other parties, these interests are included as non-controlling interests. The Partnership uses the equity method of accounting for its investments in entities over which it is able to exercise significant influence.
Basis of Presentation - Transactions between entities under common control	Acquisitions by the Partnership from TC Energy are considered common control transactions. If businesses are acquired from TC Energy that will be consolidated by the Partnership, the historical consolidated financial statements are required to be recast, except net income per common unit, to include the acquired entities for all periods presented. If the Partnership acquires an asset or an investment from TC Energy, which will be accounted for by the equity method, the financial information is not required to be recast and the transaction is accounted for prospectively from the date of the acquisition. U.S. federal and certain state income taxes are the responsibility of the partners and are not reflected in these consolidated financial statements. The tax effect of the Partnership's activities accrues to its partners. The Partnership's taxable income or loss, which may vary substantially from the net income or loss reported in the consolidated statement of operations, is includable in the U.S. federal income tax returns of each partner. In instances where the Partnership's consolidated entities are subject to state income taxes, the asset-liability method is used to account for taxes. This method requires the recognition of deferred tax assets and liabilities for future tax consequences attributable to the differences between the financial statement carrying amount of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are classified as non-current on our consolidated balance sheet.
Use of Estimates	Use of Estimates The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities, if any, as of the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Although management believes these estimates are reasonable, actual results could differ from these estimates.

EQUITY INVESTMENTS (Tables)

3 Months Ended

Mar. 31, 2019

EQUITY INVESTMENTS

Schedule of equity investments and summarized financial information for equity investees


	Ownership		Equity Earnings		Equity Investments
	Interest at		Three months
(unaudited)	March 31,		Ended March 31,		March 31,	December 31,
(millions of dollars)	2019		2019	2018	2019	2018

Northern Border	50	%	21	17	489	497
Great Lakes	46.45	%	20	24	498	489
Iroquois	49.34	%	13	18	209	210
			54	59	1,196	1,196

Northern Border

EQUITY INVESTMENTS

Schedule of equity investments and summarized financial information for equity investees


(unaudited)
(millions of dollars)	March 31, 2019	December 31, 2018

ASSETS
Cash and cash equivalents	14	10
Other current assets	38	36
Property, plant and equipment, net	1,023	1,037
Other assets	13	13
	1,088	1,096

LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	41	34
Deferred credits and other	35	35
Long-term debt, net (a)	264	264
Partners’ equity
Partners’ capital	749	764
Accumulated other comprehensive loss	(1)	(1)
	1,088	1,096


	Three months ended
(unaudited)	March 31,
(millions of dollars)	2019	2018

Transmission revenues	81	72
Operating expenses	(20)	(19)
Depreciation	(15)	(15)
Financial charges and other	(4)	(4)
Net income	42	34

(a)No current maturities as of March 31, 2019 and December 31, 2018. At March 31, 2019, Northern Border is in compliance with all its financial covenants.

Great Lakes

EQUITY INVESTMENTS

Schedule of equity investments and summarized financial information for equity investees


(unaudited)
(millions of dollars)	March 31, 2019	December 31, 2018

ASSETS
Current assets	86	75
Property, plant and equipment, net	685	689
	771	764

LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	25	26
Net long-term debt, including current maturities (a)	229	240
Other long-term liabilities	4	4
Partners' equity	513	494
	771	764


	Three months ended
(unaudited)	March 31,
(millions of dollars)	2019	2018

Transmission revenues	72	81
Operating expenses	(16)	(17)
Depreciation	(8)	(8)
Financial charges and other	(4)	(4)
Net income	44	52

(a) Includes current maturities of $21 million as of March 31, 2019 and as of December 31, 2018. At March 31, 2019, Great Lakes is in compliance with all its financial covenants.

Iroquois

EQUITY INVESTMENTS

Schedule of equity investments and summarized financial information for equity investees


(unaudited)
(millions of dollars)	March 31, 2019	December 31, 2018

ASSETS
Cash and cash equivalents	84	80
Other current assets	30	32
Property, plant and equipment, net	576	581
Other assets	16	8
	706	701

LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	19	19
Long-term debt, net (a)	325	325
Other non-current liabilities	20	14
Partners' equity	342	343
	706	701


	Three months ended
(unaudited)	March 31,
(millions of dollars)	2019	2018

Transmission revenues	52	60
Operating expenses	(15)	(14)
Depreciation	(7)	(7)
Financial charges and other	(3)	(4)
Net income	27	35

^(a)

Includes current maturities of $146 million as of March 31, 2019 and as of December 31, 2018. At March 31, 2019, Iroquois is in compliance with all its financial covenants.

DEBT AND CREDIT FACILITIES (Tables)

3 Months Ended

Mar. 31, 2019

DEBT AND CREDIT FACILITIES

Schedule of debt and credit facilities


		Weighted Average				Weighted Average
		Interest Rate for the				Interest Rate for the
(unaudited)		Three Months Ended			December 31,	Year Ended
(millions of dollars)	March 31, 2019	March 31, 2019			2018	December 31, 2018
TC PipeLines, LP
Senior Credit Facility due 2021	—	3.61	%		40	3.14	%
2013 Term Loan Facility due 2022	500	3.73	%		500	3.23	%
4.65% Unsecured Senior Notes due 2021	350	4.65	%	(a)	350	4.65	%	(a)
4.375% Unsecured Senior Notes due 2025	350	4.375	%	(a)	350	4.375	%	(a)
3.90 % Unsecured Senior Notes due 2027	500	3.90	%	(a)	500	3.90	%	(a)
GTN
5.29% Unsecured Senior Notes due 2020	100	5.29	%	(a)	100	5.29	%	(a)
5.69% Unsecured Senior Notes due 2035	150	5.69	%	(a)	150	5.69	%	(a)
Unsecured Term Loan Facility due 2019	35	3.45	%		35	2.93	%
PNGTS
Revolving Credit Facility due 2023	27	3.75	%		19	3.55	%
Tuscarora
Unsecured Term Loan due 2020	24	3.63	%		24	3.10	%
North Baja
Unsecured Term Loan due 2021	50	3.56	%		50	3.54	%
	2,086				2,118
Less: unamortized debt issuance costs and debt discount	10				10
Less: current portion	36				36
	2,040				2,072

(a) Fixed interest rate

Schedule of principal repayments required on debt


(unaudited)
(millions of dollars)		Principal payments
2019		36
2020		123
2021		400
2022		500
2023		27
Thereafter		1,000
		2,086

NET INCOME PER COMMON UNIT (Tables)

3 Months Ended

Mar. 31, 2019

NET INCOME PER COMMON UNIT

Schedule of net income per common unit



(unaudited)	Three months ended March 31,
(millions of dollars, except per common unit amounts)	2019		2018

Net income attributable to controlling interests		93		96
Net income attributable to the General Partner		(2)		(2)
Net income attributable to common units		91		94
Weighted average common units outstanding (millions) – basic and diluted		71.3		71.2
Net income per common unit – basic and diluted	$	1.28	$	1.32

CHANGE IN OPERATING WORKING CAPITAL (Tables)

3 Months Ended

Mar. 31, 2019

CHANGE IN OPERATING WORKING CAPITAL

Schedule of change in operating working capital


(unaudited)	Three months ended March 31,
(millions of dollars)	2019	2018

Change in accounts receivable and other	7	—
Change in inventories	(1)	—
Change in other current assets	2	(3)
Change in accounts payable and accrued liabilities	(4)	—
Change in accounts payable to affiliates	1	—
Change in accrued interest	8	9
Change in operating working capital	13	6

RELATED PARTY TRANSACTIONS (Tables)

3 Months Ended

Mar. 31, 2019

RELATED PARTY TRANSACTIONS

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


	Three months ended
(unaudited)	March 31,
(millions of dollars)	2019	2018

Capital and operating costs charged by TC Energy’s subsidiaries to:
Great Lakes (a)	11	9
Northern Border (a)	9	9
GTN	10	8
Bison	1	2
North Baja	1	1
Tuscarora	1	1
PNGTS (a)	2	2
Impact on the Partnership’s net income:
Great Lakes	5	4
Northern Border	4	4
GTN	8	8
Bison	1	2
North Baja	1	1
Tuscarora	1	1
PNGTS	1	1

^(a)

Represents 100 percent of the costs.

Summary of amount payable to related party for costs charged


(unaudited)
(millions of dollars)	March 31, 2019	December 31, 2018

Net amounts payable to TC Energy’s subsidiaries are as follows:
Great Lakes (a)	5	3
Northern Border (a)	4	3
GTN	4	4
Bison	—	1
North Baja	1	—
Tuscarora	—	1
PNGTS (a)	1	1

^(a)

Represents 100 percent of the costs.

ACCOUNTS RECEIVABLE AND OTHER (Tables)

3 Months Ended

Mar. 31, 2019

ACCOUNTS RECEIVABLE AND OTHER

Schedule of accounts receivable and other


(unaudited)
(millions of dollars)	March 31, 2019	December 31, 2018

Trade accounts receivable, net of allowance of nil	35	44
Imbalance receivable from affiliates	4	2
Other	2	2
	41	48

FINANCIAL CHARGES AND OTHER (Tables)

3 Months Ended

Mar. 31, 2019

FINANCIAL CHARGES AND OTHER

Schedule of components of financial charges and other


	Three months ended
(unaudited)	March 31,
(millions of dollars)	2019	2018

Interest expense (a)	23	24
Net realized gain related to the interest rate swaps	(1)	(1)
	22	23

^(a)

Includes amortization of debt issuance costs and discount costs.

VARIABLE INTEREST ENTITIES (Tables)

3 Months Ended

Mar. 31, 2019

VARIABLE INTEREST ENTITIES

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


(unaudited)
(millions of dollars)	March 31, 2019	December 31, 2018

ASSETS (LIABILITIES) (a)
Cash and cash equivalents	25	16
Accounts receivable and other	37	39
Inventories	9	8
Other current assets	5	6
Equity investments	1,196	1,196
Property, plant and equipment, net	1,237	1,240
Other assets	1	1
Accounts payable and accrued liabilities	(26)	(33)
Accounts payable to affiliates, net	(38)	(40)
Accrued interest	(5)	(2)
Current portion of long-term debt	(36)	(36)
Long-term debt	(349)	(341)
Other liabilities	(28)	(27)
Deferred state income tax	(9)	(9)

^(a)

- Definition

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

+ References + Details

ORGANIZATION - Ownership Interests in Natural Gas Pipeline Systems (Details)	3 Months Ended
	Mar. 31, 2019 LimitedPartnership
ORGANIZATION
Number of intermediate limited partnerships through which pipeline assets are owned	3

ACCOUNTING PRONOUNCEMENTS - Leases (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019
ACCOUNTING PRONOUNCEMENTS
Operating ROU assets	$ 0.5	$ 0.6
Operating lease liabilities	$ 0.5	$ 0.6
Weighted average remaining term (in years)	2 years 7 months 17 days
Discount rate (in percent)	3.57%

REGULATORY (Details) - FERC - item	Apr. 04, 2019	Mar. 15, 2019	Feb. 28, 2019
Iroquois
REGULATORY
Reduction of existing maximum system rates (as a percent)			6.50%
Number phases of reduction of rates			2
Reduction of existing maximum system rates effective March 1,2019 (as a percent)			3.25%
Reduction of existing maximum system rates effective April 1,2020 (as a percent)			3.25%
Tuscarora Settlement
REGULATORY
Reduction of existing maximum system rates (as a percent)		1.70%
Additional decrease of unit rate (as a percent)		10.80%
Northern Border
REGULATORY
Decrease in rate (as a percent)	2.00%

EQUITY INVESTMENTS (Details) - USD ($) $ in Millions			3 Months Ended
EQUITY INVESTMENTS (Details) - USD ($) $ in Millions	May 01, 2019	Apr. 24, 2019	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
EQUITY INVESTMENTS
Equity Earnings			$ 54	$ 59
Equity Investments			1,196		$ 1,196
Equity contribution			5	4
LIABILITIES AND PARTNERS' EQUITY
Current portion of long-term debt (Note 7)			36		36
Distributions from Equity Investments
Distributions received from equity investments			58	45
Distributions from equity investments			56	43
Return on investment distribution classified as investing activities			2	2
Great Lakes
EQUITY INVESTMENTS
Total cash call issued to fund debt repayment			$ 11
Iroquois
EQUITY INVESTMENTS
Ownership interest (as a percent)	49.34%		49.34%
Distributions from Equity Investments
Distributions from equity investments	$ 14		$ 14	14
Return on investment distribution classified as investing activities	$ 2		$ 2	2
Limited partners, Distribution declared		$ 28
Northern Border
EQUITY INVESTMENTS
Ownership interest (as a percent)			50.00%
Equity Earnings			$ 21	17
Equity Investments			489		497
ASSETS
Cash and cash equivalents			14		10
Other current assets			38		36
Property, plant and equipment, net			1,023		1,037
Other assets			13		13
Assets, total			1,088		1,096
LIABILITIES AND PARTNERS' EQUITY
Current liabilities			41		34
Deferred credits and other			35		35
Net long-term debt, including current maturities			264		264
Current portion of long-term debt (Note 7)			0		0
Partners' capital			749		764
Accumulated other comprehensive loss			(1)		(1)
Liabilities and Partners' Equity, total			1,088		1,096
Revenues (expenses)
Transmission revenues			81	72
Operating expenses			(20)	(19)
Depreciation			(15)	(15)
Financial charges and other			(4)	(4)
Net income			$ 42	34
Great Lakes
EQUITY INVESTMENTS
Ownership interest (as a percent)			46.45%
Equity Earnings			$ 20	24
Equity Investments			498		489
Equity contribution			5	4
ASSETS
Current assets			86		75
Property, plant and equipment, net			685		689
Assets, total			771		764
LIABILITIES AND PARTNERS' EQUITY
Current liabilities			25		26
Net long-term debt, including current maturities			229		240
Current portion of long-term debt (Note 7)			21		21
Other non-current liabilities			4		4
Partners' capital			513		494
Liabilities and Partners' Equity, total			771		764
Revenues (expenses)
Transmission revenues			72	81
Operating expenses			(16)	(17)
Depreciation			(8)	(8)
Financial charges and other			(4)	(4)
Net income			$ 44	52
Iroquois
EQUITY INVESTMENTS
Ownership interest (as a percent)			49.34%
Equity Earnings			$ 13	18
Equity Investments			209		210
ASSETS
Cash and cash equivalents			84		80
Other current assets			30		32
Property, plant and equipment, net			576		581
Other assets			16		8
Assets, total			706		701
LIABILITIES AND PARTNERS' EQUITY
Current liabilities			19		19
Net long-term debt, including current maturities			325		325
Current portion of long-term debt (Note 7)			146		146
Other non-current liabilities			20		14
Partners' capital			342		343
Liabilities and Partners' Equity, total			706		$ 701
Revenues (expenses)
Transmission revenues			52	60
Operating expenses			(15)	(14)
Depreciation			(7)	(7)
Financial charges and other			(3)	(4)
Net income			$ 27	$ 35

REVENUES - Contract Balances (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Contract Balances
Receivables from contracts with customers	$ 35	$ 44

DEBT AND CREDIT FACILITIES - Amounts Outstanding and Description of Terms (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Credit facilities, short-term loan facility and long-term debt
Total credit facilities, short-term loan facility and long-term debt	$ 2,086	$ 2,118
Less: unamortized debt issuance costs and debt discount	10	10
Less: current portion	36	36
Long-term debt	$ 2,040	2,072
Senior Credit Facility due in 2021 and the Term Loan Facilities due in 2022
Credit facilities, short-term loan facility and long-term debt
Leverage ratio, actual (as a percent)	3.03%
Senior Credit Facility due in 2021 and the Term Loan Facilities due in 2022 \| Each fiscal quarter except fiscal quarter and the two following fiscal quarters in which one or more acquisitions has been executed \| Maximum
Credit facilities, short-term loan facility and long-term debt
Leverage ratio, covenant (as a percent)	5.00%
Senior Credit Facility due in 2021 and the Term Loan Facilities due in 2022 \| Fiscal quarter and the two following fiscal quarters in which one or more acquisitions has been executed \| Maximum
Credit facilities, short-term loan facility and long-term debt
Leverage ratio, covenant (as a percent)	5.50%
Revolving credit facility \| TC PipeLines, LP Senior Credit Facility due 2021
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities		$ 40
Weighted average interest rate (as a percent)	3.61%	3.14%
Maximum borrowing capacity	$ 500
Amount outstanding under credit facility	0	$ 40
Revolving credit facility \| TC PipeLines, LP Senior Credit Facility due 2021 \| LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end (as a percent)		3.77%
Term loan \| TC PipeLines, LP 2013 Term Loan Facility due 2022
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	$ 500	$ 500
Weighted average interest rate (as a percent)	3.73%	3.23%
Term loan \| TC PipeLines, LP 2013 Term Loan Facility due 2022 \| LIBOR borrowings \| LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end (as a percent)	3.74%	3.60%
Term loan \| TC PipeLines, LP 2013 Term Loan Facility due 2022 \| LIBOR borrowings \| LIBOR \| Hedges of cash flows \| Interest rate swaps
Credit facilities, short-term loan facility and long-term debt
Weighted average interest rate (as a percent)	3.26%	3.26%
Unsecured debt \| TC PipeLines, LP 4.65% Senior Notes due 2021
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	$ 350	$ 350
Stated interest rate (as a percent)	4.65%
Weighted average interest rate (as a percent)	4.65%	4.65%
Unsecured debt \| TC PipeLines, LP 4.375% Senior Notes due 2025
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	$ 350	$ 350
Stated interest rate (as a percent)	4.375%
Weighted average interest rate (as a percent)	4.375%	4.375%
Unsecured debt \| TC PipeLines, LP 3.90% Senior Notes due 2027
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	$ 500	$ 500
Stated interest rate (as a percent)	3.90%
Weighted average interest rate (as a percent)	3.90%	3.90%
Unsecured debt \| GTN 5.29% Senior Notes due 2020
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	5.29%
Unsecured debt \| GTN 5.69% Senior Notes due 2035
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	5.69%
Unsecured debt \| Tuscarora Term Loan due 2020
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	$ 24	$ 24
Weighted average interest rate (as a percent)	3.63%	3.10%
Unsecured debt \| North Baja Term Loan Due 2021
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	$ 50	$ 50
Weighted average interest rate (as a percent)	3.56%	3.54%
Unsecured debt \| North Baja Term Loan Due 2021 \| LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end (as a percent)	3.56%	3.54%
GTN \| Unsecured debt \| GTN 5.29% Senior Notes due 2020
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	$ 100	$ 100
Weighted average interest rate (as a percent)	5.29%	5.29%
GTN \| Unsecured debt \| GTN 5.69% Senior Notes due 2035
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	$ 150	$ 150
Weighted average interest rate (as a percent)	5.69%	5.69%
GTN \| Unsecured debt \| Term Loan Facility due 2019
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	$ 35	$ 35
Weighted average interest rate (as a percent)	3.45%	2.93%
Percentage of debt to total capitalization, covenant	42.50%
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 interest rate, at period end (as a percent)	3.44%	3.30%
PNGTS \| Secured debt \| PNGTS Revolving Credit Facility due 2023
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities	$ 27	$ 19
Weighted average interest rate (as a percent)	3.75%	3.55%
Leverage ratio, covenant (as a percent)	0.47%
PNGTS \| Secured debt \| PNGTS Revolving Credit Facility due 2023 \| Maximum
Credit facilities, short-term loan facility and long-term debt
Leverage ratio, covenant (as a percent)	5.00%
PNGTS \| Secured debt \| PNGTS Revolving Credit Facility due 2023 \| LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end (as a percent)	3.74%	3.60%
Tuscarora \| Unsecured debt \| Tuscarora Term Loan due 2020
Credit facilities, short-term loan facility and long-term debt
Debt service coverage, covenant (as a percent)	10.14%
Tuscarora \| Unsecured debt \| Tuscarora Term Loan due 2020 \| Minimum
Credit facilities, short-term loan facility and long-term debt
Debt service coverage, covenant (as a percent)	3.00%
Tuscarora \| Unsecured debt \| Tuscarora Term Loan due 2020 \| LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end (as a percent)	3.61%	3.47%
North Baja \| Unsecured debt \| North Baja Term Loan Due 2021
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization, actual	38.11%
North Baja \| Unsecured debt \| North Baja Term Loan Due 2021 \| Maximum
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization, covenant	70.00%

DEBT AND CREDIT FACILITIES - Principal Repayments Required (Details) $ in Millions	Mar. 31, 2019 USD ($)
Principal repayments required on debt
2019	$ 36
2020	123
2021	400
2022	500
2023	27
Thereafter	1,000
Total debt	$ 2,086

PARTNERS' EQUITY - ATM Equity Issuance Program (Details)	3 Months Ended
	Mar. 31, 2019 shares
ATM Equity Issuance Program \| Common units
PARTNERS' EQUITY
Units sold	0

PARTNERS' EQUITY - Class B Units (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
PARTNERS' EQUITY
Limited Partners, Distributions paid	$ 13	$ 15
Distributions \| Class B units
PARTNERS' EQUITY
Limited Partners, Distributions paid	$ 13
TC Energy \| Distributions \| Class B units
PARTNERS' EQUITY
Percentage of reduction in distributions payable	35.00%
TC Energy \| Distributions \| Common units
PARTNERS' EQUITY
Percentage of reduction in distributions payable	35.00%
Minimum distribution payable per common unit	$ 3.94
GTN \| TC Energy \| Distributions \| Class B units
PARTNERS' EQUITY
Portion of GTN's annual distributions to which the Class B units are entitled to receive a percentage share of the distributions above threshold (as a percent)	30.00%
Percentage applied to 30 percent of GTN's distributions above threshold for the year ending December 31, 2019	100.00%
Threshold of GTN's total distributable cash flows for payment to Class B units for the year ending December 31, 2019	$ 20
Percentage applied to 30 percent of GTN's distributions above threshold for the year ending December 31, 2020	43.75%
Threshold of GTN's total distributable cash flows for payment to Class B units for the year ending December 31, 2020	$ 20
Percentage applied to 30 percent of GTN's distributions above threshold thereafter	25.00%
Threshold of GTN's distributions for payment to Class B units	$ 20		$ 20	$ 20

NET INCOME PER COMMON UNIT - General Partner Effective Interest and Allocated Incentive Distributions (Details)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
General Partner \| General Partner
PARTNERS' EQUITY
General partner interest (as a percent)	2.00%	2.00%

NET INCOME PER COMMON UNIT- Terms of Class B Unit Distributions and Determination of Net Income (Loss) per Common Unit (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Net income per common unit
Net income attributable to controlling interests	$ 93	$ 96
Net income attributable to the General Partner	(2)	(2)
Class B units
Net income per common unit
Net income attributable to common units	0	0
Common units
Net income per common unit
Net income attributable to common units	$ 91	$ 94
Weighted average common units outstanding - basic (in units)	71.3	71.2
Weighted average common units outstanding - diluted (in units)	71.3	71.2
Net income (loss) per common unit - basic (in dollars per unit)	$ 1.28	$ 1.32
Net income (loss) per common unit - diluted (in dollars per unit)	$ 1.28	$ 1.32
GTN \| Class B units \| TC Energy \| Distributions
Distributions
Percentage applied to GTN's distributable cash flow	30.00%
GTN's distributions for payment to Class B units	$ 20		$ 20	$ 20

CASH DISTRIBUTIONS PAID TO COMMON UNITS (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Common units
Partners' Equity
Per Unit Distribution, paid (in dollars per unit)	$ 0.65	$ 1.00
Total cash distribution	$ 47	$ 76
General Partner \| General Partner
Partners' Equity
Total distribution for General Partner interest	$ 1	$ 2
General partner interest (as a percent)	2.00%	2.00%
General Partner \| Common units and General Partner interest combined
Partners' Equity
Incentive distribution paid to the General Partner		$ 3

CHANGE IN OPERATING WORKING CAPITAL - Components (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
CHANGE IN OPERATING WORKING CAPITAL
Change in accounts receivable and other	$ 7
Change in inventories	(1)
Change in other current assets	2	$ (3)
Change in accounts payable and accrued liabilities	(4)
Change in accounts payable to affiliates	1
Change in accrued interest	8	9
Change in operating working capital	$ 13	$ 6

RELATED PARTY TRANSACTIONS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	$ 7			$ 6
Amount included in receivables from related party	4			2
General Partner \| Reimbursement of costs of services provided
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	1		$ 1
TC Energy \| Great Lakes
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	$ 5			3
Percentage of capital and operating costs charged	100.00%		100.00%
Amount included in receivables from related party	$ 18			18
TC Energy \| Great Lakes \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	11		$ 9
Impact on the Partnership's net income attributable to controlling interests	$ 5		$ 4
Percentage of capital and operating costs charged	100.00%		100.00%
TC Energy \| Great Lakes \| Transportation contracts \| Total net revenues \| Customer concentration risk
Capital and operating costs charged to the pipeline systems and amount payable
Percent of total revenues	73.00%		68.00%
TC Energy \| Northern Border
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	$ 4			3
Percentage of capital and operating costs charged	100.00%		100.00%
TC Energy \| Northern Border \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	$ 9		$ 9
Impact on the Partnership's net income attributable to controlling interests	$ 4		$ 4
Percentage of capital and operating costs charged	100.00%		100.00%
TC Energy \| PNGTS
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	$ 1			1
Percentage of capital and operating costs charged	100.00%		100.00%
TC Energy \| PNGTS \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	$ 2		$ 2
Impact on the Partnership's net income attributable to controlling interests	$ 1		$ 1
Percentage of capital and operating costs charged	100.00%		100.00%
TC Energy \| PNGTS \| Transportation contracts
Capital and operating costs charged to the pipeline systems and amount payable
Amount included in receivables from related party	$ 0			0
Revenues from related party	0		$ 1
TC Energy \| GTN
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	4			4
TC Energy \| GTN \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	10		8
Impact on the Partnership's net income attributable to controlling interests	8		8
TC Energy \| Bison
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable				1
TC Energy \| Bison \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	1		2
Impact on the Partnership's net income attributable to controlling interests	1		2
TC Energy \| North Baja
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	1
TC Energy \| North Baja \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	1		1
Impact on the Partnership's net income attributable to controlling interests	1		1
TC Energy \| Tuscarora
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable				$ 1
TC Energy \| Tuscarora \| Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	1		1
Impact on the Partnership's net income attributable to controlling interests	1		$ 1
ANR Pipeline Company \| Great Lakes \| Transportation contracts
Capital and operating costs charged to the pipeline systems and amount payable
Contract term		15 years
Total contract value		$ 1,300
Affiliates \| PNGTS \| Construction of facilities
Capital and operating costs charged to the pipeline systems and amount payable
Reimbursement of costs	$ 71

FAIR VALUE MEASUREMENTS - Estimated Fair Value of Debt (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value \| Level 2
Financial Instruments
Fair value of debt	$ 2,119	$ 2,101

FAIR VALUE MEASUREMENTS - Interest Rate Swaps (Details) - Interest rate swaps - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Term loan \| TC PipeLines, LP 2013 Term Loan Facility due 2022
Interest rate derivatives
Weighted average fixed interest rate (as a percent)	3.26%
Hedges of cash flows
Interest rate derivatives
Change in fair value of interest rate derivative instruments recognized in other comprehensive income (loss)	$ (5)	$ 7
Hedges of cash flows \| Financial charges and other
Interest rate derivatives
Net realized gain related to the interest rate swaps included in financial charges and other	1	$ 1
Hedges of cash flows \| Recurring fair value measurement \| Level 2
Interest rate derivatives
Fair value of derivative asset, gross	3		$ 8
Fair value of derivative asset, net	$ 3		$ 8

ACCOUNTS RECEIVABLE AND OTHER (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
ACCOUNTS RECEIVABLE AND OTHER
Trade accounts receivable, net of allowance of nil	$ 35	$ 44
Imbalance receivable from affiliates	4	2
Other	2	2
Accounts receivable and other	41	48
Trade accounts receivable, allowance	$ 0	$ 0

FINANCIAL CHARGES AND OTHER (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
FINANCIAL CHARGES AND OTHER
Interest expense	$ 23	$ 24
Net realized gain related to the interest rate swaps	(1)	(1)
Financial charges and other	$ 22	$ 23

VARIABLE INTEREST ENTITIES - Consolidated VIEs (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
ASSETS (LIABILITIES)
Cash and cash equivalents	$ 52	$ 33
Accounts receivable and other	41	48
Inventories	9	8
Other current assets	5	8
Equity investments	1,196	1,196
Property, plant and equipment, net	1,522	1,529
Other assets	3	6
Accounts payable and accrued liabilities	(29)	(36)
Accounts payable to affiliates, net	(7)	(6)
Accrued interest	(20)	(12)
Current portion of long-term debt	(36)	(36)
Long-term debt	(2,040)	(2,072)
Other liabilities	(31)	(29)
Consolidated VIEs \| Restricted VIEs
ASSETS (LIABILITIES)
Cash and cash equivalents	25	16
Accounts receivable and other	37	39
Inventories	9	8
Other current assets	5	6
Equity investments	1,196	1,196
Property, plant and equipment, net	1,237	1,240
Other assets	1	1
Accounts payable and accrued liabilities	(26)	(33)
Accounts payable to affiliates, net	(38)	(40)
Accrued interest	(5)	(2)
Current portion of long-term debt	(36)	(36)
Long-term debt	(349)	(341)
Other liabilities	(28)	(27)
Deferred state income tax	$ (9)	$ (9)

SUBSEQUENT EVENTS - Distributions (Details) - USD ($) $ / shares in Units, $ in Millions								3 Months Ended
	May 13, 2019	May 01, 2019	Apr. 30, 2019	Apr. 24, 2019	Apr. 23, 2019	Apr. 16, 2019	Apr. 09, 2019	Mar. 31, 2019	Mar. 31, 2018
Distributions
Limited Partners, Distributions paid								$ 13	$ 15
Partnership's share of distributions								$ 56	$ 43
Northern Border
Distributions
Ownership interest (as a percent)								50.00%
Great Lakes
Distributions
Ownership interest (as a percent)								46.45%
Subsequent Events \| Northern Border
Distributions
Ownership interest (as a percent)			50.00%
Partnership's share of distributions			$ 7
Subsequent Events \| Great Lakes
Distributions
Ownership interest (as a percent)		46.45%
Partnership's share of distributions		$ 23
Subsequent Events \| Iroquois
Distributions
Ownership interest (as a percent)		49.34%
Partnership's share of distributions		$ 14
Interest in unrestricted cash		$ 2
Subsequent Events \| Northern Border
Distributions
Limited partners, Distribution declared							$ 15
Subsequent Events \| Great Lakes
Distributions
Limited partners, Distribution declared						$ 49
Subsequent Events \| Iroquois
Distributions
Limited partners, Distribution declared				$ 28
Subsequent Events \| PNGTS
Distributions
Limited partners, Distribution declared							$ 19
Share of distributions to its non-controlling interest owner			$ 7
General Partner \| General Partner
Distributions
Ownership interest in the Partnership (as a percent)								2.00%	2.00%
Forecast \| Subsequent Events
Distributions
Limited Partners, Distributions paid	$ 47
Distribution to General Partner	1
Common units \| Subsequent Events
Distributions
Per Unit Distribution, declared (in dollars per unit)					$ 0.65
Common units \| Subsequent Events \| General Partner
Distributions
Ownership interest in the Partnership (as a percent)					2.00%
Common units \| General Partner \| Subsequent Events
Distributions
Number of units held by investor			5,797,106
Common units \| TC Energy \| Subsequent Events
Distributions
Number of units held by investor			11,287,725
Common units \| Forecast \| Subsequent Events
Distributions
Limited Partners, Distributions paid	46
Common units \| Forecast \| General Partner \| Subsequent Events
Distributions
Limited Partners, Distributions paid	4
Common units \| Forecast \| TC Energy \| Subsequent Events
Distributions
Limited Partners, Distributions paid	$ 7