TC Pipelines (TCP) 10-Q 6 May 20 2020 Q1 Quarterly report Financial data

COVER PAGE

COVER PAGE - shares	3 Months Ended
	Mar. 31, 2020	May 04, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Mar. 31, 2020
Entity File Number	001-35358
Entity Registrant Name	TC PipeLines, LP
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	52-2135448
Entity Address, Address Line One	700 Louisiana Street,
Entity Address, Address Line Two	Suite 700
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77002-2761
City Area Code	877
Local Phone Number	290-2772
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Title of 12(b) Security	Common units representing limited partner interests
Trading Symbol	TCP
Security Exchange Name	NYSE
Entity Common Stock, Shares Outstanding		71,306,396
Entity Central Index Key	0001075607
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Transmission revenues	$ 101	$ 113
Equity earnings (Note 5)	55	54
Operation and maintenance expenses	(16)	(16)
Property taxes	(6)	(7)
General and administrative	(1)	(2)
Depreciation and amortization	(20)	(20)
Financial charges and other (Note 15)	(19)	(22)
Net income before taxes	94	100
Income taxes	0	0
Net income	94	100
Net income attributable to non-controlling interest	6	7
Net income attributable to controlling interests	88	93
Net income attributable to controlling interest allocation (Note 9)
Common units	86	91
General Partner	2	2
Net income attributable to controlling interests	$ 88	$ 93
Net income per common unit (Note 9) - basic and diluted (in dollars per unit)	$ 1.21	$ 1.28
Weighted average common units outstanding — basic and diluted (millions)	71.3	71.3
Common units outstanding, end of period (millions)	71.3	71.3

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 94	$ 100
Other comprehensive income
Change in fair value of cash flow hedges (Note 13)	(13)	(5)
Reclassification to net income of gains and losses on cash flow hedges	0	0
Comprehensive income	81	95
Comprehensive income attributable to non-controlling interests	6	7
Comprehensive income attributable to controlling interests	$ 75	$ 88

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Current Assets
Cash and cash equivalents	$ 134	$ 83
Accounts receivable and other (Note 14)	37	43
Distribution receivable from Iroquois	0	14
Inventories	11	10
Other	3	6
Total current assets	185	156
Equity investments (Note 5)	1,102	1,098
Property, plant and equipment (Net of $1,201 accumulated depreciation; 2019 - $1,187)	1,540	1,528
Goodwill	71	71
TOTAL ASSETS	2,898	2,853
Current Liabilities
Accounts payable and accrued liabilities	33	28
Accounts payable to affiliates (Note 12)	6	8
Accrued interest	20	11
Current portion of long-term debt (Note 7)	123	123
Total current liabilities	182	170
Long-term debt, net (Note 7)	1,887	1,880
Deferred state income taxes	7	7
Other liabilities	43	36
Total liabilities	2,119	2,093
Partners’ Equity
General partner	15	14
Accumulated other comprehensive income (loss) (AOCI)	(18)	(5)
Controlling interests	676	656
Non-controlling interests	103	104
Total partners' equity	779	760
TOTAL LIABILITIES AND PARTNERS’ EQUITY	2,898	2,853
Common Units
Partners’ Equity
Limited partner	584	544
Class B Units
Partners’ Equity
Limited partner	$ 95	$ 103

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Accumulated depreciation	$ 1,201	$ 1,187

CONSOLIDATED STATEMENT OF CASH

CONSOLIDATED STATEMENT OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash Generated from Operations
Net income	$ 94	$ 100
Depreciation and amortization	20	20
Equity earnings from equity investments (Note 5)	(55)	(54)
Distributions received from operating activities of equity investments (Note 5)	65	56
Change in operating working capital (Note 11)	9	13
Other	(2)	0
Cash Generated from Operations	131	135
Investing Activities
Investment in Great Lakes (Note 5)	(5)	(5)
Distribution received from Iroquois as return of investment (Note 5)	5	2
Capital expenditures	(24)	(16)
Customer advances for construction	0	2
Investing Activities	(24)	(17)
Financing Activities
Distributions paid to common units, including the General Partner (Note 10)	(47)	(47)
Distributions paid to Class B units (Note 8)	(8)	(13)
Distributions paid to non-controlling interests	(7)	(7)
Long-term debt issued, net of discount (Note 7)	6	18
Long-term debt repaid (Note 7)	0	(50)
Financing Activities	(56)	(99)
Increase in cash and cash equivalents	51	19
Cash and cash equivalents, beginning of period	83	33
Cash and cash equivalents, end of period	$ 134	$ 52

CONSOLIDATED STATEMENT OF CHANG

CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY - 3 months ended Mar. 31, 2020 - USD ($) shares in Millions, $ in Millions	Total	Non- Controlling Interest	Accumulated Other Comprehensive Income (Loss)	[1]	Limited PartnersCommon Units	Limited PartnersClass B Units	General Partner
Partners' Equity at beginning of period at Dec. 31, 2019	$ 760	$ 104	$ (5)		$ 544	$ 103	$ 14
Partners' Equity at beginning of period (in units) at Dec. 31, 2019					71.3	1.9
Increase (Decrease) in Partners' Equity
Net income	94	6			$ 86		2
Other comprehensive income (loss)	(13)		(13)
Distributions	(62)	(7)			(46)	$ (8)	(1)
Partners' Equity at end of period at Mar. 31, 2020	$ 779	$ 103	$ (18)		$ 584	$ 95	$ 15
Partners' Equity at end of period (in units) at Mar. 31, 2020					71.3	1.9
[1]	Gain (loss) related to cash flow hedges reported in AOCI and expected to be reclassified to Net income in the next 12 months is estimated to be $(8) million . These estimates assume constant interest rates over time; however, the amounts reclassified will vary based on actual value of interest rates at the date of settlement.

CONSOLIDATED STATEMENT OF CHA_2

CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY (Parenthetical) $ in Millions	3 Months Ended
	Mar. 31, 2020USD ($)
Statement of Partners' Capital [Abstract]
Loss related to cash flow hedges in AOCI expected to be reclassified to Net income in the next 12 months	$ 8

ORGANIZATION

ORGANIZATION	3 Months Ended
	Mar. 31, 2020
Limited Liability Company or Limited Partnership, Business Organization and Operations [Abstract]
ORGANIZATION	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 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.

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
SIGNIFICANT ACCOUNTING POLICIES	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, 2020 and 2019 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, 2019 included in our 2019 Annual Report. 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 2019 Annual Report, except those that became effective in 2020 as described in full under 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. U.S. federal and certain state income taxes are the responsibility of the limited partners and are not reflected in these consolidated financial statements. The tax effect of the Partnership's activities accrues to its limited 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 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 sheets. 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

ACCOUNTING PRONOUNCEMENTS	3 Months Ended
	Mar. 31, 2020
Accounting Changes and Error Corrections [Abstract]
ACCOUNTING PRONOUNCEMENTS	ACCOUNTING PRONOUNCEMENTS Changes in Accounting Policies effective January 1, 2020 Measurement of credit losses on financial instruments In June 2016, the Financial Accounting Standards Board (FASB) issued new guidance that 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 became effective January 1, 2020 and was applied using a modified retrospective approach. The adoption of this new guidance did not have a material impact on the Partnership’s 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 became effective January 1, 2020, and was applied on a retrospective basis. The adoption of this new guidance did not have a material impact on the Partnership’s consolidated financial statements. Reference rate reform In March 2020, in response to the expected cessation of LIBOR,the FASB issued new optional guidance that eases the potential burden of accounting for reference rate reform. The new guidance provides optional expedients for contracts and hedging relationships that are affected by reference rate reform, if certain criteria are met. Each of the expedients can be applied as of January 1, 2020 through December 31, 2022. For eligible hedging relationships existing as of January 1, 2020 and prospectively, the Partnership has applied the optional expedient allowing an entity to assume that the hedged forecasted transaction in a cash flow hedge is probable of occurring. As reference rate reform is still an ongoing process, the Partnership will continue to evaluate the timing and potential impact of adoption of other optional expedients when deemed necessary.

GOODWILL

GOODWILL	3 Months Ended
	Mar. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL	GOODWILL Consistent with GAAP, we evaluate our goodwill related to Tuscarora and North Baja for impairment at least annually and if any indicators of impairment are evident. In 2019, based on our analysis of Tuscarora and North Baja’s current market conditions, we believed there to be a greater than 50 percent likelihood that Tuscarora and North Baja’s estimated fair value exceeded their carrying value. As a result, at December 31, 2019, we did not identify an impairment on the $ 71 million of goodwill related to the Tuscarora ($ 23 million ) and North Baja ($ 48 million ) acquisitions. During the first quarter of 2020 there were two major events that impacted financial markets and global economic activity. First, there was an outbreak of a novel strain of coronavirus, COVID-19, which spread around the world and was declared a global pandemic on March 11, 2020 by the World Health Organization (WHO). Second, shortly after the outbreak, the global oil market experienced a precipitous decline in the price of crude oil due to an oversupply of oil coupled with significant demand concerns due to the economic impacts of the COVID-19 pandemic. We believe the current state of the macroeconomic environment does not represent a permanent shift although it is difficult to predict the severity of the impact of these events or how long any disruptions are likely to continue. Additionally, the following factors were considered in our analysis specific to the Partnership's Tuscarora and North Baja reporting units: • the long-term natural gas price futures relevant to gas transported on Tuscarora and North Baja do not reflect material differences from what was forecast in 2019; • at least 90 percent of Tuscarora and North Baja's revenue is tied to long-term take-or-pay, fixed price contracts which have a low correlation to short-term changes in demand; • Tuscarora and North Baja have not experienced any customer defaults to date and have significant collateral in support of their contracts; • multiples and discount rate assumptions used in our quantitative model are reflective of our long-term outlook for Tuscarora and North Baja, in line with their underlying asset life, versus the shorter-term nature of the current situation; and • while we may experience a slowdown in some of our construction activities, the expansion projects associated with these assets are materially on track, and we do not anticipate any significant changes in outlook or delay or inability to proceed due to financing requirements. As a result of these factors, at March 31, 2020, we believe there is a greater than 50 percent likelihood that both Tuscarora’s and North Baja’s estimated fair values continue to exceed their carrying values. Therefore, no impairment exists on our goodwill. However, adverse changes to our key considerations could result in future impairments on our goodwill.

EQUITY INVESTMENTS

EQUITY INVESTMENTS	3 Months Ended
	Mar. 31, 2020
Equity Method Investments and Joint Ventures [Abstract]
EQUITY INVESTMENTS	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 Northern Border and Great Lakes pipeline systems 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. Ownership Equity Earnings Equity Investments Interest at Three months ended (unaudited) March 31, March 31, March 31, December 31, (millions of dollars) 2020 2020 2019 2020 2019 Northern Border 50.00% 22 21 416 422 Great Lakes 46.45% 20 20 501 491 Iroquois 49.34% 13 13 185 185 55 54 1,102 1,098 Distributions from Equity Investments Distributions received from equity investments in the three months ended March 31, 2020 totaled $71 million ( March 31, 2019 - $58 million ), of which $5.2 million ( March 31, 2019 - $2.6 million ), was considered return of capital and 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 During the three months ended March 31, 2020 , the Partnership received distributions from Northern Border amounting to $28 million ( March 31, 2019 - $28 million ). The Partnership did not have undistributed earnings from Northern Border for the three months ended March 31, 2020 and 2019 . The summarized financial information provided to us by Northern Border is as follows: (unaudited) (millions of dollars) March 31, 2020 December 31, 2019 ASSETS Cash and cash equivalents 25 21 Other current assets 38 37 Property, plant and equipment, net 979 989 Other assets 12 12 1,054 1,059 LIABILITIES AND PARTNERS’ EQUITY Current liabilities 47 42 Deferred credits and other 40 39 Long-term debt, net (a) 364 364 Partners’ equity Partners’ capital 604 615 Accumulated other comprehensive loss (1 ) (1 ) 1,054 1,059 Three months ended (unaudited) March 31, (millions of dollars) 2020 2019 Transmission revenues 83 81 Operating expenses (20 ) (20 ) Depreciation (15 ) (15 ) Financial charges and other (4 ) (4 ) Net income 44 42 (a) No current maturities as of March 31, 2020 and December 31, 2019 . At March 31, 2020 , Northern Border was in compliance with all its financial covenants. Great Lakes, a variable interest entity The Partnership is considered to have a variable interest in Great Lakes, which is accounted for as equity investment since we are not its primary beneficiary. A variable interest entity is a legal entity that either does not have sufficient equity at risk to finance its activities without additional subordinated financial support, 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. The Partnership made an equity contribution to Great Lakes of $5 million during the three months ended March 31, 2020 ( March 31, 2019 - $5 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. During the three months ended March 31, 2020 , the Partnership received distributions from Great Lakes amounting to $16 million ( March 31, 2019 - $17 million ). The Partnership did not have undistributed earnings from Great Lakes for the three months ended March 31, 2020 and 2019 . The summarized financial information provided to us by Great Lakes is as follows: (unaudited) (millions of dollars) March 31, 2020 December 31, 2019 ASSETS Current assets 78 72 Property, plant and equipment, net 684 685 762 757 LIABILITIES AND PARTNERS’ EQUITY Current liabilities 28 33 Net long-term debt, including current maturities (a) 208 219 Other long term liabilities 7 6 Partners’ equity 519 499 762 757 Three months ended (unaudited) March 31, (millions of dollars) 2020 2019 Transmission revenues 72 72 Operating expenses (16 ) (16 ) Depreciation (8 ) (8 ) Financial charges and other (4 ) (4 ) Net income 44 44 (a) Includes current maturities of $31 million as of March 31, 2020 ( December 31, 2019 - $21 million ). At March 31, 2020 , Great Lakes was in compliance with all its financial covenants. Iroquois During the three months ended March 31, 2020 , the Partnership received distributions from Iroquois amounting to $27 million ( March 31, 2019 - $13 million ), which includes the Partnership’s 49.34 percent share of the Iroquois unrestricted cash distribution amounting to approximately $5.2 million ( March 31, 2019 - $2.6 million ). The unrestricted cash did not represent a distribution of Iroquois’ cash from operations during the period and therefore it was reported as a return of investment in the Partnership’s consolidated statement of cash flows. The Partnership did not have undistributed earnings from Iroquois for the three months ended March 31, 2020 and 2019 . The summarized financial information provided to us by Iroquois is as follows: (unaudited) (millions of dollars) March 31, 2020 December 31, 2019 ASSETS Cash and cash equivalents 32 43 Other current assets 86 36 Property, plant and equipment, net 515 570 Other assets 17 16 650 665 LIABILITIES AND PARTNERS’ EQUITY Current liabilities 21 34 Long-term debt, net (a) 317 317 Other non-current liabilities 19 20 Partners’ equity 293 294 650 665 Three months ended (unaudited) March 31, (millions of dollars) 2020 2019 Transmission revenues 52 52 Operating expenses (15 ) (15 ) Depreciation (8 ) (7 ) Financial charges and other (3 ) (3 ) Net income 26 27 (a) Includes current maturities of $3 million as of March 31, 2020 ( December 31, 2019 - $3 million ). At March 31, 2020 , Iroquois was in compliance with all of its financial covenants.

REVENUES

REVENUES	3 Months Ended
	Mar. 31, 2020
Revenue from Contract with Customer [Abstract]
REVENUES	REVENUES Disaggregation of Revenues For the three months ended March 31, 2020 and 2019 , 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, 2020 , 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 $34 million at March 31, 2020 ( December 31, 2019 - $37 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, "Accounts Receivable and Other"). Additionally, our accounts receivable represent the Partnership’s unconditional right to consideration for services completed which includes billed and unbilled accounts. Right to invoice practical expedient 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

DEBT AND CREDIT FACILITIES	3 Months Ended
	Mar. 31, 2020
Debt Disclosure [Abstract]
DEBT AND CREDIT FACILITIES	DEBT AND CREDIT FACILITIES (unaudited) (millions of dollars) March 31, 2020 Weighted Average Interest Rate for the Three Months Ended March 31, 2020 December 31, 2019 Weighted Average Interest Rate for the Year Ended December 31, 2019 TC PipeLines, LP Senior Credit Facility due 2021 — — — — 2013 Term Loan Facility due 2022 450 2.93% 450 3.52% 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) PNGTS Revolving Credit Facility due 2023 45 2.92% 39 3.47% Tuscarora Unsecured Term Loan due 2020 23 2.80% 23 3.39% North Baja Unsecured Term Loan due 2021 50 2.75% 50 3.34% 2,018 2,012 Less: unamortized debt issuance costs and debt discount 8 9 Less: current portion 123 123 1,887 1,880 (a) Fixed interest rate TC PipeLines, LP The Partnership’s senior facility under revolving credit agreement as amended and restated, dated September 29, 2017 (Senior Credit Facility) consists of a $500 million senior revolving credit facility with a banking syndicate, maturing November 10, 2021. In March 2019, the Partnership repaid all amounts outstanding under its Senior Credit Facility and there was no outstanding balance at March 31, 2020 and December 31, 2019 . As of March 31, 2020 , the variable interest rate exposure related to the term loan facility under a term loan agreement, as amended, dated September 29, 2017 (2013 Term Loan Facility) was hedged using interest rate swaps at an average rate of 3.26 percent ( December 31, 2019 - 3.26 percent ). Prior to hedging activities, the London Interbank Offered Rate based (LIBOR) interest rate on the 2013 Term Loan Facility was 2.83 percent at March 31, 2020 ( December 31, 2019 - 2.94 percent ). The Senior Credit Facility and the 2013 Term Loan Facility require the Partnership to maintain a debt to adjusted cash flow leverage ratio of 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 have been executed, in which case the leverage ratio is to be no greater than 5.50 to 1.00 . The leverage ratio was 3.41 to 1.00 as of March 31, 2020 . GTN GTN’s $100 million 5.29% Unsecured Senior Notes due June 1, 2020 (Unsecured Senior Notes) 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, 2020 was 38.7 percent . GTN’s $100 million 5.29% Unsecured Senior Notes due June 1, 2020 are expected to be refinanced together with additional funding to be used to finance a portion of GTN XPress. PNGTS PNGTS’ Revolving Credit Facility requires PNGTS to maintain a leverage ratio not greater than 5.00 to 1.00. The leverage ratio was 0.86 to 1.00 as of March 31, 2020 . During the three months ended March 31, 2020, PNGTS borrowed an additional $ 6 million on its Revolving Credit Facility to fund its expansion projects. The LIBOR-based interest rate applicable to PNGTS’s Revolving Credit Facility was 2.83 percent at March 31, 2020 ( December 31, 2019 - 2.99 percent ). Tuscarora Tuscarora’s $ 23 million variable rate Unsecured Term Loan due August 1, 2020 (Unsecured Term Loan) contains a covenant that requires Tuscarora to maintain a debt service coverage ratio (cash available from operations divided by the sum of interest expense and principal payments) of greater than or equal to 3.00 to 1.00. As of March 31, 2020 , the ratio was 8.63 to 1.00. The LIBOR-based interest rate applicable to Tuscarora’s Unsecured Term Loan Facility was 2.71 percent at March 31, 2020 ( December 31, 2019 - 2.82 percent ). Tuscarora's Unsecured Term Loan is due August 21, 2020 and is expected to be refinanced together with additional funding to be used to finance a portion of Tuscarora XPress. 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, 2020 was 39.99 percent . The LIBOR-based interest rate applicable to North Baja’s Term Loan Facility was 2.66 percent at March 31, 2020 ( December 31, 2019 - 2.77 percent ). Partnership (TC PipeLines, LP and its subsidiaries) At March 31, 2020 , the Partnership was in compliance with all terms and conditions including its financial covenants and its other covenants including restrictions on entering into mergers, consolidations and sales of assets, granting of liens, material amendments to the Fourth Amended and Restated Agreement of Limited Partnership, as amended to date (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 2020 123 2021 400 2022 450 2023 45 2024 — Thereafter 1,000 2,018

PARTNERS' EQUITY

PARTNERS' EQUITY	3 Months Ended
	Mar. 31, 2020
Partners' Capital Notes [Abstract]
PARTNERS' EQUITY	PARTNERS’ EQUITY 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 through March 31, 2020 and (ii) 25 percent of distributions above $20 million thereafter , which equates to 43.75 percent of distributions above $20 million for the year ending December 31, 2020 (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 to 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 ending December 31, 2020, 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 2021. During the three months ended March 31, 2020 , the 2020 annual Class B Distribution threshold was not exceeded. For the year ended December 31, 2019, the Class B Distribution was $8 million and was declared and paid in the first quarter of 2020.

NET INCOME PER COMMON UNIT

NET INCOME PER COMMON UNIT	3 Months Ended
	Mar. 31, 2020
Earnings Per Share [Abstract]
NET INCOME PER COMMON UNIT	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 2020 will equal 30 percent of GTN’s distributable cash flow during the year ending December 31, 2020 less $20 million , the residual of which is further multiplied by 43.75 percent . This amount is further reduced by the estimated Class B Reduction for 2020 , an approximately 35 percent reduction applied to the estimated annual Class B Distribution ( December 31, 2019 - $20 million less Class B Reduction). During the three months ended March 31, 2020 and 2019, 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) 2020 2019 Net income attributable to controlling interests 88 93 Net income attributable to the General Partner (2 ) (2 ) Net income attributable to common units 86 91 Weighted average common units outstanding (millions) — basic and diluted 71.3 71.3 Net income per common unit — basic and diluted $1.21 $1.28

CASH DISTRIBUTIONS PAID TO COMM

CASH DISTRIBUTIONS PAID TO COMMON UNITS	3 Months Ended
	Mar. 31, 2020
Partners' Capital Account, Distributions [Abstract]
CASH DISTRIBUTIONS PAID TO COMMON UNITS	CASH DISTRIBUTIONS PAID TO COMMON UNITS During the three months ended March 31, 2020 and 2019, the Partnership distributed $0.65 per common unit for a total distribution of $47 million each quarter. The total distribution paid includes our General Partner's share for its two percent general partner interest totaling $1 million . The General Partner did not receive any distributions in respect of its IDRs during the three months ended March 31, 2020 and 2019.

CHANGE IN OPERATING WORKING CAP

CHANGE IN OPERATING WORKING CAPITAL	3 Months Ended
	Mar. 31, 2020
Supplemental Cash Flow Elements [Abstract]
CHANGE IN OPERATING WORKING CAPITAL	CHANGE IN OPERATING WORKING CAPITAL (unaudited) Three months ended March 31, (millions of dollars) 2020 2019 Change in accounts receivable and other (a) 3 7 Change in inventories (1 ) (1 ) Change in other current assets 3 2 Change in accounts payable and accrued liabilities (a) (3 ) (4 ) Change in accounts payable to affiliates (2 ) 1 Change in accrued interest 9 8 Change in operating working capital 9 13 (a) Excludes certain non-cash items primarily related to capital accruals and credits.

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS	3 Months Ended
	Mar. 31, 2020
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	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, 2020 and 2019, total costs charged to the Partnership by the General Partner were $1 million . As operator of our pipelines, except Iroquois and a certain portion of the PNGTS facilities, 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, "Equity Investments"). Capital and operating costs charged to our pipeline systems, except for Iroquois, for the three months ended March 31, 2020 and 2019 by TC Energy’s subsidiaries and amounts payable to TC Energy’s subsidiaries at March 31, 2020 and December 31, 2019 are summarized in the following tables: Three months ended (unaudited) March 31, (millions of dollars) 2020 2019 Capital and operating costs charged by TC Energy’s subsidiaries to: Great Lakes (a) 11 11 Northern Border (a) 10 9 GTN 12 10 Bison — 1 North Baja 1 1 Tuscarora 1 1 PNGTS (a) 2 2 Impact on the Partnership’s income (b) : Great Lakes 4 5 Northern Border 4 4 GTN 8 8 Bison — 1 North Baja 1 1 Tuscarora 1 1 PNGTS 1 1 (unaudited) (millions of dollars) March 31, 2020 December 31, 2019 Net amounts payable to TC Energy’s subsidiaries are as follows: Great Lakes (a) 4 5 Northern Border (a) 3 4 GTN 5 5 Bison — — North Baja — 1 Tuscarora — — PNGTS (a) 1 1 (a) Represents 100 percent of the costs. (b) Represents the Partnership's proportionate share based ownership percentage of these pipelines. 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, 2020 , Great Lakes earned 74 percent of its transportation revenues from TC Energy and its affiliates ( March 31, 2019 - 73 percent ). At March 31, 2020 , $18 million was included in Great Lakes’ receivables with regard to the transportation contracts with TC Energy and its affiliates ( December 31, 2019 - $19 million ). In 2018, Great Lakes executed long-term transportation capacity contracts with its affiliate, ANR Pipeline Company (ANR) in anticipation of specific possible future needs. The original total contract value of these contracts was approximately $1.3 billion over a 15-year period. These contracts were subject to certain conditions and provisions, including a reduction option up to the full contract quantity if exercised up to certain date. During the first quarter of 2020, several amendments were made to these contracts and ANR exercised the right to terminate a significant portion of the contracts amounting to approximately $1.1 billion . The remaining maximum rate contract, which has a total capacity of approximately 168,000 Dth/Day and total contract value of $182 million over a term of 20 years , is expected to begin in late 2022. This contract, which has a full quantity reduction option at any time before October 1, 2022, is dependent on ANR being able to secure the required regulatory approvals and other requirements of the project associated with these volumes. The remaining unsubscribed capacity on Great Lakes will be available for contracting in response to developing marketing conditions. PNGTS In connection with the Portland XPress expansion project (PXP), which was designed to be phased in over a three year time period, PNGTS has entered into an arrangement with its affiliates regarding the construction of certain facilities on their systems that are required to fulfill future contracts on the PNGTS system. PXP Phases I and II were placed into service on November 1, 2018 and November 1, 2019, respectively. Phase III is anticipated to be in service on November 1, 2020. In the event the expansions are terminated prior to their in-service dates, PNGTS will be required to reimburse its affiliates for any costs incurred related to the development of their facilities. As a result of placing the TC Energy facilities associated with the Phase II volumes in service, PNGTS' obligation to reimburse these development costs has largely been fulfilled. PNGTS is currently obligated to reimburse costs incurred by TC Energy in relation to Phase III, which was approximately $1.5 million at March 31, 2020 and estimated to be approximately $8.6 million by November 1, 2020, when Phase III goes into service.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	3 Months Ended
	Mar. 31, 2020
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	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, 2020 and December 31, 2019 was $1,967 million and $2,111 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, 2020 , the fair value of the interest rate swaps accounted for as cash flow hedges was a liability of $19 million (both on a gross and net basis) ( December 31, 2019 - liability of $6 million ), the net change of which is recognized in other comprehensive income. For the three months ended March 31, 2020 , the net realized gain related to the interest rate swaps was nil and was included in "financial charges and other" ( March 31, 2019 - gain of $ 1 million ) (Refer to Note 15, "Financial Charges and Other'). The Partnership has no master netting agreements; however, it has derivative contracts containing provisions with rights of offset. The Partnership has elected to present the fair value of derivative instruments with the right to offset on a gross basis in the 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, 2020 and December 31, 2019 .

ACCOUNTS RECEIVABLE AND OTHER

ACCOUNTS RECEIVABLE AND OTHER	3 Months Ended
	Mar. 31, 2020
Receivables [Abstract]
ACCOUNTS RECEIVABLE AND OTHER	ACCOUNTS RECEIVABLE AND OTHER (unaudited) (millions of dollars) March 31, 2020 December 31, 2019 Trade accounts receivable, net of allowance of nil 34 37 Imbalance receivable from affiliates — — Other 3 6 37 43

FINANCIAL CHARGES AND OTHER

FINANCIAL CHARGES AND OTHER	3 Months Ended
	Mar. 31, 2020
Other Expense, Nonoperating [Abstract]
FINANCIAL CHARGES AND OTHER	FINANCIAL CHARGES AND OTHER Three months ended (unaudited) March 31, (millions of dollars) 2020 2019 Interest expense (a) 20 23 Net realized gain related to the interest rate swaps — (1 ) Other income (1 ) — 19 22 (a) Includes amortization of debt issuance costs and discount costs.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	3 Months Ended
	Mar. 31, 2020
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS Management of the Partnership has reviewed subsequent events through May 6, 2020, 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 21, 2020, the board of directors of the General Partner declared the Partnership’s first quarter 2020 cash distribution in the amount of $0.65 per common unit payable on May 12, 2020 to unitholders of record as of May 1, 2020. 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 of 2020 . Northern Border declared its March 2020 distribution of $16 million on April 7, 2020, of which the Partnership received its 50 percent share or $8 million on April 30, 2020. Great Lakes declared its first quarter 2020 distribution of $46 million on April 15, 2020, of which the Partnership received its 46.45 percent share or $21 million on April 30, 2020. Iroquois declared its first quarter 2020 distribution of $21 million on May 1, 2020, of which the Partnership will receive its 49.34 percent share or $11 million on June 29, 2020. PNGTS declared its first quarter 2020 distribution of $16 million on April 7, 2020, of which $6 million

SIGNIFICANT ACCOUNTING POLICI_2

SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Basis of Accounting	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, 2020 and 2019 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, 2019 included in our 2019 Annual Report. 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 2019 Annual Report, except those that became effective in 2020 as described in full under Note 3, "Accounting Pronouncements".
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	U.S. federal and certain state income taxes are the responsibility of the limited partners and are not reflected in these consolidated financial statements. The tax effect of the Partnership's activities accrues to its limited 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 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 sheets.
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.
Changes in Accounting Policies	Changes in Accounting Policies effective January 1, 2020 Measurement of credit losses on financial instruments In June 2016, the Financial Accounting Standards Board (FASB) issued new guidance that 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 became effective January 1, 2020 and was applied using a modified retrospective approach. The adoption of this new guidance did not have a material impact on the Partnership’s 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 became effective January 1, 2020, and was applied on a retrospective basis. The adoption of this new guidance did not have a material impact on the Partnership’s consolidated financial statements. Reference rate reform In March 2020, in response to the expected cessation of LIBOR,the FASB issued new optional guidance that eases the potential burden of accounting for reference rate reform. The new guidance provides optional expedients for contracts and hedging relationships that are affected by reference rate reform, if certain criteria are met. Each of the expedients can be applied as of January 1, 2020 through December 31, 2022. For eligible hedging relationships existing as of January 1, 2020 and prospectively, the Partnership has applied the optional expedient allowing an entity to assume that the hedged forecasted transaction in a cash flow hedge is probable of occurring. As reference rate reform is still an ongoing process, the Partnership will continue to evaluate the timing and potential impact of adoption of other optional expedients when deemed necessary.

EQUITY INVESTMENTS (Tables)

EQUITY INVESTMENTS (Tables)	3 Months Ended
	Mar. 31, 2020
Equity Method Investments and Joint Ventures [Abstract]
Summary of equity investments	The summarized financial information provided to us by Northern Border is as follows: (unaudited) (millions of dollars) March 31, 2020 December 31, 2019 ASSETS Cash and cash equivalents 25 21 Other current assets 38 37 Property, plant and equipment, net 979 989 Other assets 12 12 1,054 1,059 LIABILITIES AND PARTNERS’ EQUITY Current liabilities 47 42 Deferred credits and other 40 39 Long-term debt, net (a) 364 364 Partners’ equity Partners’ capital 604 615 Accumulated other comprehensive loss (1 ) (1 ) 1,054 1,059 Three months ended (unaudited) March 31, (millions of dollars) 2020 2019 Transmission revenues 83 81 Operating expenses (20 ) (20 ) Depreciation (15 ) (15 ) Financial charges and other (4 ) (4 ) Net income 44 42 (a) No current maturities as of March 31, 2020 and December 31, 2019 . At March 31, 2020 , Northern Border was in compliance with all its financial covenants. Ownership Equity Earnings Equity Investments Interest at Three months ended (unaudited) March 31, March 31, March 31, December 31, (millions of dollars) 2020 2020 2019 2020 2019 Northern Border 50.00% 22 21 416 422 Great Lakes 46.45% 20 20 501 491 Iroquois 49.34% 13 13 185 185 55 54 1,102 1,098 The summarized financial information provided to us by Great Lakes is as follows: (unaudited) (millions of dollars) March 31, 2020 December 31, 2019 ASSETS Current assets 78 72 Property, plant and equipment, net 684 685 762 757 LIABILITIES AND PARTNERS’ EQUITY Current liabilities 28 33 Net long-term debt, including current maturities (a) 208 219 Other long term liabilities 7 6 Partners’ equity 519 499 762 757 Three months ended (unaudited) March 31, (millions of dollars) 2020 2019 Transmission revenues 72 72 Operating expenses (16 ) (16 ) Depreciation (8 ) (8 ) Financial charges and other (4 ) (4 ) Net income 44 44 (a) Includes current maturities of $31 million as of March 31, 2020 ( December 31, 2019 - $21 million ). At March 31, 2020 , Great Lakes was in compliance with all its financial covenants. The summarized financial information provided to us by Iroquois is as follows: (unaudited) (millions of dollars) March 31, 2020 December 31, 2019 ASSETS Cash and cash equivalents 32 43 Other current assets 86 36 Property, plant and equipment, net 515 570 Other assets 17 16 650 665 LIABILITIES AND PARTNERS’ EQUITY Current liabilities 21 34 Long-term debt, net (a) 317 317 Other non-current liabilities 19 20 Partners’ equity 293 294 650 665 Three months ended (unaudited) March 31, (millions of dollars) 2020 2019 Transmission revenues 52 52 Operating expenses (15 ) (15 ) Depreciation (8 ) (7 ) Financial charges and other (3 ) (3 ) Net income 26 27 (a) Includes current maturities of $3 million as of March 31, 2020 ( December 31, 2019 - $3 million ). At March 31, 2020 , Iroquois was in compliance with all of its financial covenants.

DEBT AND CREDIT FACILITIES (Tab

DEBT AND CREDIT FACILITIES (Tables)	3 Months Ended
	Mar. 31, 2020
Debt Disclosure [Abstract]
Schedule of debt and credit facilities	(unaudited) (millions of dollars) March 31, 2020 Weighted Average Interest Rate for the Three Months Ended March 31, 2020 December 31, 2019 Weighted Average Interest Rate for the Year Ended December 31, 2019 TC PipeLines, LP Senior Credit Facility due 2021 — — — — 2013 Term Loan Facility due 2022 450 2.93% 450 3.52% 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) PNGTS Revolving Credit Facility due 2023 45 2.92% 39 3.47% Tuscarora Unsecured Term Loan due 2020 23 2.80% 23 3.39% North Baja Unsecured Term Loan due 2021 50 2.75% 50 3.34% 2,018 2,012 Less: unamortized debt issuance costs and debt discount 8 9 Less: current portion 123 123 1,887 1,880 (a) Fixed interest rate
Schedule of principal repayments required on debt	The principal repayments required of the Partnership on its debt are as follows: (unaudited) (millions of dollars) Principal Payments 2020 123 2021 400 2022 450 2023 45 2024 — Thereafter 1,000 2,018

NET INCOME PER COMMON UNIT (Tab

NET INCOME PER COMMON UNIT (Tables)	3 Months Ended
	Mar. 31, 2020
Earnings Per Share [Abstract]
Schedule of net income per common unit	Net income per common unit was determined as follows: (unaudited) Three months ended March 31, (millions of dollars, except per common unit amounts) 2020 2019 Net income attributable to controlling interests 88 93 Net income attributable to the General Partner (2 ) (2 ) Net income attributable to common units 86 91 Weighted average common units outstanding (millions) — basic and diluted 71.3 71.3 Net income per common unit — basic and diluted $1.21 $1.28

CHANGE IN OPERATING WORKING C_2

CHANGE IN OPERATING WORKING CAPITAL (Tables)	3 Months Ended
	Mar. 31, 2020
Supplemental Cash Flow Elements [Abstract]
Schedule of change in operating working capital	(unaudited) Three months ended March 31, (millions of dollars) 2020 2019 Change in accounts receivable and other (a) 3 7 Change in inventories (1 ) (1 ) Change in other current assets 3 2 Change in accounts payable and accrued liabilities (a) (3 ) (4 ) Change in accounts payable to affiliates (2 ) 1 Change in accrued interest 9 8 Change in operating working capital 9 13 (a) Excludes certain non-cash items primarily related to capital accruals and credits.

RELATED PARTY TRANSACTIONS (Tab

RELATED PARTY TRANSACTIONS (Tables)	3 Months Ended
	Mar. 31, 2020
Related Party Transactions [Abstract]
Summary of related party transactions	Capital and operating costs charged to our pipeline systems, except for Iroquois, for the three months ended March 31, 2020 and 2019 by TC Energy’s subsidiaries and amounts payable to TC Energy’s subsidiaries at March 31, 2020 and December 31, 2019 are summarized in the following tables: Three months ended (unaudited) March 31, (millions of dollars) 2020 2019 Capital and operating costs charged by TC Energy’s subsidiaries to: Great Lakes (a) 11 11 Northern Border (a) 10 9 GTN 12 10 Bison — 1 North Baja 1 1 Tuscarora 1 1 PNGTS (a) 2 2 Impact on the Partnership’s income (b) : Great Lakes 4 5 Northern Border 4 4 GTN 8 8 Bison — 1 North Baja 1 1 Tuscarora 1 1 PNGTS 1 1 (unaudited) (millions of dollars) March 31, 2020 December 31, 2019 Net amounts payable to TC Energy’s subsidiaries are as follows: Great Lakes (a) 4 5 Northern Border (a) 3 4 GTN 5 5 Bison — — North Baja — 1 Tuscarora — — PNGTS (a) 1 1 (a) Represents 100 percent of the costs. (b) Represents the Partnership's proportionate share based ownership percentage of these pipelines.

ACCOUNTS RECEIVABLE AND OTHER (

ACCOUNTS RECEIVABLE AND OTHER (Tables)	3 Months Ended
	Mar. 31, 2020
Receivables [Abstract]
Schedule of accounts receivable and other	(unaudited) (millions of dollars) March 31, 2020 December 31, 2019 Trade accounts receivable, net of allowance of nil 34 37 Imbalance receivable from affiliates — — Other 3 6 37 43

FINANCIAL CHARGES AND OTHER (Ta

FINANCIAL CHARGES AND OTHER (Tables)	3 Months Ended
	Mar. 31, 2020
Other Expense, Nonoperating [Abstract]
Schedule of components of financial charges and other	Three months ended (unaudited) March 31, (millions of dollars) 2020 2019 Interest expense (a) 20 23 Net realized gain related to the interest rate swaps — (1 ) Other income (1 ) — 19 22 (a) Includes amortization of debt issuance costs and discount costs.

GOODWILL (Details)

GOODWILL (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Goodwill	$ 71	$ 71
Tuscarora
Goodwill [Line Items]
Goodwill		23
North Baja
Goodwill [Line Items]
Goodwill		$ 48

EQUITY INVESTMENTS - Summary of

EQUITY INVESTMENTS - Summary of equity investments (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Equity Earnings	$ 55,000,000	$ 54,000,000
Equity Investments	$ 1,102,000,000		$ 1,098,000,000
Northern Border
Schedule of Equity Method Investments [Line Items]
Ownership Interest	50.00%
Equity Earnings	$ 22,000,000	21,000,000
Equity Investments	416,000,000		422,000,000
ASSETS
Cash and cash equivalents	25,000,000		21,000,000
Other current assets	38,000,000		37,000,000
Property, plant and equipment, net	979,000,000		989,000,000
Other assets	12,000,000		12,000,000
Assets, total	1,054,000,000		1,059,000,000
LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	47,000,000		42,000,000
Deferred credits and other	40,000,000		39,000,000
Net long-term debt, including current maturities	364,000,000		364,000,000
Partners’ capital	604,000,000		615,000,000
Accumulated other comprehensive loss	(1,000,000)		(1,000,000)
Liabilities and Partners' Equity, total	1,054,000,000		1,059,000,000
NET INCOME
Transmission revenues	83,000,000	81,000,000
Operating expenses	(20,000,000)	(20,000,000)
Depreciation	(15,000,000)	(15,000,000)
Financial charges and other	(4,000,000)	(4,000,000)
Net income	44,000,000	42,000,000
Long-term debt current maturities	$ 0		0
Great Lakes
Schedule of Equity Method Investments [Line Items]
Ownership Interest	46.45%
Equity Earnings	$ 20,000,000	20,000,000
Equity Investments	501,000,000		491,000,000
ASSETS
Current assets	78,000,000		72,000,000
Property, plant and equipment, net	684,000,000		685,000,000
Assets, total	762,000,000		757,000,000
LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	28,000,000		33,000,000
Net long-term debt, including current maturities	208,000,000		219,000,000
Other long term liabilities	7,000,000		6,000,000
Partners’ capital	519,000,000		499,000,000
Liabilities and Partners' Equity, total	762,000,000		757,000,000
NET INCOME
Transmission revenues	72,000,000	72,000,000
Operating expenses	(16,000,000)	(16,000,000)
Depreciation	(8,000,000)	(8,000,000)
Financial charges and other	(4,000,000)	(4,000,000)
Net income	44,000,000	44,000,000
Long-term debt current maturities	$ 31,000,000		21,000,000
Iroquois
Schedule of Equity Method Investments [Line Items]
Ownership Interest	49.34%
Equity Earnings	$ 13,000,000	13,000,000
Equity Investments	185,000,000		185,000,000
ASSETS
Cash and cash equivalents	32,000,000		43,000,000
Other current assets	86,000,000		36,000,000
Property, plant and equipment, net	515,000,000		570,000,000
Other assets	17,000,000		16,000,000
Assets, total	650,000,000		665,000,000
LIABILITIES AND PARTNERS’ EQUITY
Current liabilities	21,000,000		34,000,000
Net long-term debt, including current maturities	317,000,000		317,000,000
Other long term liabilities	19,000,000		20,000,000
Partners’ capital	293,000,000		294,000,000
Liabilities and Partners' Equity, total	650,000,000		665,000,000
NET INCOME
Transmission revenues	52,000,000	52,000,000
Operating expenses	(15,000,000)	(15,000,000)
Depreciation	(8,000,000)	(7,000,000)
Financial charges and other	(3,000,000)	(3,000,000)
Net income	26,000,000	$ 27,000,000
Long-term debt current maturities	$ 3,000,000		$ 3,000,000

EQUITY INVESTMENTS - Narrative

EQUITY INVESTMENTS - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Schedule of Equity Method Investments [Line Items]
Distributions received from equity investments	$ 71	$ 58
Return on investment distribution classified as investing activities	5	2
Equity contribution	5	5
Partnership's share of distributions	65	56
Northern Border
Schedule of Equity Method Investments [Line Items]
Distributions received from equity investments	$ 28	28
Ownership interest	50.00%
Great Lakes
Schedule of Equity Method Investments [Line Items]
Distributions received from equity investments	$ 16	17
Equity contribution	$ 5	5
Ownership interest	46.45%
Iroquois
Schedule of Equity Method Investments [Line Items]
Return on investment distribution classified as investing activities	$ 5.2	2.6
Ownership interest	49.34%
Partnership's share of distributions	$ 27	13
Great Lakes
Schedule of Equity Method Investments [Line Items]
Total cash call issued to fund debt repayment	11
Iroquois
Schedule of Equity Method Investments [Line Items]
Return on investment distribution classified as investing activities	$ 5.2	$ 2.6

REVENUES - Contract Balances (D

REVENUES - Contract Balances (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Contract Balances
Receivables from contracts with customers	$ 34	$ 37

DEBT AND CREDIT FACILITIES - Sc

DEBT AND CREDIT FACILITIES - Schedule of debt and credit facilities (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Debt, gross	$ 2,018	$ 2,012
Less: unamortized debt issuance costs and debt discount	8	9
Less: current portion	123	123
Debt, net	1,887	1,880
Revolving credit facility | Senior Credit Facility due 2021
Debt Instrument [Line Items]
Debt, gross	$ 0	$ 0
Weighted average interest rate	0.00%	0.00%
Term loan | 2013 Term Loan Facility due 2022
Debt Instrument [Line Items]
Debt, gross	$ 450	$ 450
Weighted average interest rate	2.93%	3.52%
Unsecured debt | 4.65% Unsecured Senior Notes due 2021
Debt Instrument [Line Items]
Stated interest rate	4.65%
Debt, gross	$ 350	$ 350
Weighted average interest rate	4.65%	4.65%
Unsecured debt | 4.375% Unsecured Senior Notes due 2025
Debt Instrument [Line Items]
Stated interest rate	4.375%
Debt, gross	$ 350	$ 350
Weighted average interest rate	4.375%	4.375%
Unsecured debt | 3.90 % Unsecured Senior Notes due 2027
Debt Instrument [Line Items]
Stated interest rate	3.90%
Debt, gross	$ 500	$ 500
Weighted average interest rate	3.90%	3.90%
Unsecured debt | 5.29% Unsecured Senior Notes due 2020
Debt Instrument [Line Items]
Stated interest rate	5.29%
Unsecured debt | 5.69% Unsecured Senior Notes due 2035
Debt Instrument [Line Items]
Stated interest rate	5.69%
GTN | Unsecured debt | 5.29% Unsecured Senior Notes due 2020
Debt Instrument [Line Items]
Debt, gross	$ 100	$ 100
Weighted average interest rate	5.29%	5.29%
GTN | Unsecured debt | 5.69% Unsecured Senior Notes due 2035
Debt Instrument [Line Items]
Debt, gross	$ 150	$ 150
Weighted average interest rate	5.69%	5.69%
PNGTS | Secured debt | Revolving Credit Facility due 2023
Debt Instrument [Line Items]
Debt, gross	$ 45	$ 39
Weighted average interest rate	2.92%	3.47%
Tuscarora | Unsecured debt | Unsecured Term Loan due 2020
Debt Instrument [Line Items]
Debt, gross	$ 23	$ 23
Weighted average interest rate	2.80%	3.39%
North Baja | Unsecured debt | Unsecured Term Loan due 2021
Debt Instrument [Line Items]
Debt, gross	$ 50	$ 50
Weighted average interest rate	2.75%	3.34%

DEBT AND CREDIT FACILITIES - Na

DEBT AND CREDIT FACILITIES - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Credit facilities, short-term loan facility and long-term debt
Debt, gross	$ 2,018,000,000	$ 2,012,000,000
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)	3.41%
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 | Senior Credit Facility due 2021
Credit facilities, short-term loan facility and long-term debt
Maximum borrowing capacity	$ 500,000,000
Amount outstanding under credit facility	$ 0	$ 0
Weighted average interest rate	0.00%	0.00%
Debt, gross	$ 0	$ 0
Term loan | 2013 Term Loan Facility due 2022
Credit facilities, short-term loan facility and long-term debt
Weighted average interest rate	2.93%	3.52%
Debt, gross	$ 450,000,000	$ 450,000,000
Term loan | 2013 Term Loan Facility due 2022 | Interest rate swaps
Credit facilities, short-term loan facility and long-term debt
Weighted average fixed interest rate (as a percent)	3.26%	3.26%
Term loan | 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	2.83%	2.94%
GTN | Unsecured debt | Unsecured Term Loan Facility due 2019
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization, actual	38.70%
GTN | Unsecured debt | Unsecured 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 | 5.29% Unsecured Senior Notes due 2020
Credit facilities, short-term loan facility and long-term debt
Weighted average interest rate	5.29%	5.29%
Debt, gross	$ 100,000,000	$ 100,000,000
PNGTS | Secured debt | Revolving Credit Facility due 2023
Credit facilities, short-term loan facility and long-term debt
Weighted average interest rate	2.92%	3.47%
Leverage ratio, actual (as a percent)	0.86%
Proceeds from credit facility	$ 6,000,000
Debt, gross	$ 45,000,000	$ 39,000,000
PNGTS | Secured debt | 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 | Revolving Credit Facility due 2023 | LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end	2.83%	2.99%
Tuscarora | Unsecured debt | Unsecured Term Loan due 2020
Credit facilities, short-term loan facility and long-term debt
Weighted average interest rate	2.80%	3.39%
Debt, gross	$ 23,000,000	$ 23,000,000
Debt service coverage, actual	8.63%
Tuscarora | Unsecured debt | Unsecured Term Loan due 2020 | Minimum
Credit facilities, short-term loan facility and long-term debt
Debt service coverage, covenant	3.00%
Tuscarora | Unsecured debt | Unsecured Term Loan due 2020 | LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end	2.71%	2.82%
North Baja | Unsecured debt | Unsecured Term Loan due 2021
Credit facilities, short-term loan facility and long-term debt
Weighted average interest rate	2.75%	3.34%
Percentage of debt to total capitalization, actual	39.99%
Debt, gross	$ 50,000,000	$ 50,000,000
North Baja | Unsecured debt | Unsecured Term Loan due 2021 | Maximum
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization, covenant	70.00%
North Baja | Unsecured debt | Unsecured Term Loan due 2021 | LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end	2.66%	2.77%

DEBT AND CREDIT FACILITIES - _2

DEBT AND CREDIT FACILITIES - Schedule of principal repayments required on debt (Details) $ in Millions	Mar. 31, 2020USD ($)
Principal repayments required on debt
2020	$ 123
2021	400
2022	450
2023	45
2024	0
Thereafter	1,000
Total debt	$ 2,018

PARTNERS' EQUITY (Details)

PARTNERS' EQUITY (Details) - USD ($)	3 Months Ended			12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2019
PARTNERS' EQUITY
Cash distribution	$ 8,000,000	$ 13,000,000
Distributions | Class B Units
PARTNERS' EQUITY
Cash distribution	$ 8,000,000
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 (in dollars per 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	30.00%
Percentage applied to 30 percent of GTN's distributions above threshold for the quarter ending March 31, 2020	100.00%
Threshold of GTN's total distributable cash flows for payment to Class B units for the quarter ending March 31, 2020	$ 20,000,000
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	$ 20,000,000			$ 20,000,000
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	$ 20,000,000
Percentage of reduction in distributions payable	35.00%

NET INCOME PER COMMON UNIT - Na

NET INCOME PER COMMON UNIT - Narrative (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
General Partner | General Partner | TC Pipelines, LP
PARTNERS' EQUITY
General partner interest	2.00%	2.00%
Class B Units | TC Energy | Distributions
PARTNERS' EQUITY
Percentage of reduction in distributions payable	35.00%
Class B Units | TC Energy | GTN | Distributions
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	30.00%
Threshold of GTN's distributions for payment to Class B units	$ 20,000,000		$ 20,000,000
Percentage applied to 30 percent of GTN's distributions above threshold for the year ending December 31, 2020	43.75%
Percentage of reduction in distributions payable	35.00%

NET INCOME PER COMMON UNIT - Sc

NET INCOME PER COMMON UNIT - Schedule of net income per common unit (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Net income per common unit
Net income attributable to controlling interests	$ 88	$ 93
Net income attributable to the General Partner	(2)	(2)
Net income attributable to common units	$ 86	$ 91
Weighted average common units outstanding — basic and diluted (millions)	71.3	71.3
Net income per common unit - basic and diluted (in dollars per unit)	$ 1.21	$ 1.28

CASH DISTRIBUTIONS PAID TO CO_2

CASH DISTRIBUTIONS PAID TO COMMON UNITS (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Common Units
Partners' Equity
Distribution paid (in dollars per unit)	$ 0.65	$ 0.65
Total cash distribution	$ 47	$ 47
General Partner | General Partner
Partners' Equity
Total distribution for General Partner interest	$ 1	$ 1
General Partner | General Partner | TC Pipelines, LP
Partners' Equity
General partner interest	2.00%	2.00%

CHANGE IN OPERATING WORKING C_3

CHANGE IN OPERATING WORKING CAPITAL (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Supplemental Cash Flow Elements [Abstract]
Change in accounts receivable and other	$ 3	$ 7
Change in inventories	(1)	(1)
Change in other current assets	3	2
Change in accounts payable and accrued liabilities	(3)	(4)
Change in accounts payable to affiliates	(2)	1
Change in accrued interest	9	8
Change in operating working capital	$ 9	$ 13

RELATED PARTY TRANSACTIONS - Na

RELATED PARTY TRANSACTIONS - Narrative (Details) pure_PER_D in Thousands, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020USD ($)pure / d	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Nov. 01, 2020USD ($)	Dec. 31, 2019USD ($)
Related Party Transaction [Line Items]
Amount included in receivables from related party	$ 0				$ 0
General Partner | Reimbursement of costs of services provided
Related Party Transaction [Line Items]
Costs charged	1	$ 1
Great Lakes | TC Energy
Related Party Transaction [Line Items]
Amount included in receivables from related party	18				$ 19
Great Lakes | ANR Pipeline Company | Transportation contracts
Related Party Transaction [Line Items]
Contract value	$ 182		$ 1,300
Contract term	20 years		15 years
Contract value terminated	$ 1,100
Related Party, Contract Capacity	168
Great Lakes | Customer concentration risk | Total net revenues | TC Energy | Transportation contracts
Related Party Transaction [Line Items]
Percent of total revenues	74.00%	73.00%
PNGTS | TC Energy | Portland XPress expansion project (PXP), Phase III
Related Party Transaction [Line Items]
Development costs, reimbursable	$ 1.5
PNGTS | Affiliates | Portland XPress expansion project (PXP), Phase III
Related Party Transaction [Line Items]
Phase in period	3 years
Forecast | PNGTS | TC Energy | Portland XPress expansion project (PXP), Phase III
Related Party Transaction [Line Items]
Development costs, reimbursable				$ 8.6

RELATED PARTY TRANSACTIONS - Su

RELATED PARTY TRANSACTIONS - Summary of related party transactions (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Related Party Transaction [Line Items]
Accounts payable to affiliates	$ 6		$ 8
Great Lakes | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	4		5
Great Lakes | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	11	$ 11
Impact on the Partnership's net income attributable to controlling interests	$ 4	5
Percentage of capital and operating costs charged	100.00%
Northern Border | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	$ 3		4
Northern Border | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	10	9
Impact on the Partnership's net income attributable to controlling interests	$ 4	4
Percentage of capital and operating costs charged	100.00%
GTN | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	$ 5		5
GTN | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	12	10
Impact on the Partnership's net income attributable to controlling interests	8	8
Bison | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	0		0
Bison | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	0	1
Impact on the Partnership's net income attributable to controlling interests	0	1
North Baja | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	0		1
North Baja | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	1	1
Impact on the Partnership's net income attributable to controlling interests	1	1
Tuscarora | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	0		0
Tuscarora | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	1	1
Impact on the Partnership's net income attributable to controlling interests	1	1
PNGTS | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	1		$ 1
PNGTS | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
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%

FAIR VALUE MEASUREMENTS (Detail

FAIR VALUE MEASUREMENTS (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Interest rate derivatives
Net realized gain related to the interest rate swaps included in financial charges and other	$ 0	$ 1,000,000
Interest rate swaps | Term loan | 2013 Term Loan Facility due 2022
Interest rate derivatives
Weighted average fixed interest rate (as a percent)	3.26%		3.26%
Hedges of cash flows | Recurring fair value measurement | Level 2 | Interest rate swaps
Interest rate derivatives
Fair value of derivative liability, gross	$ 19,000,000		$ 6,000,000
Fair value of derivative liability, net	19,000,000		6,000,000
Estimate of Fair Value Measurement [Member] | Level 2
Interest rate derivatives
Fair value of debt	$ 1,967,000,000		$ 2,111,000,000

ACCOUNTS RECEIVABLE AND OTHER_2

ACCOUNTS RECEIVABLE AND OTHER (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Receivables [Abstract]
Trade accounts receivable, net of allowance of nil	$ 34	$ 37
Imbalance receivable from affiliates	0	0
Other	3	6
Accounts receivable and other	$ 37	$ 43

FINANCIAL CHARGES AND OTHER (De

FINANCIAL CHARGES AND OTHER (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Other Expense, Nonoperating [Abstract]
Interest expense	$ 20,000,000	$ 23,000,000
Net realized gain related to the interest rate swaps	0	(1,000,000)
Other income	(1,000,000)	0
Financial charges and other	$ 19,000,000	$ 22,000,000

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - USD ($) $ / shares in Units, $ in Millions	Jun. 29, 2020	May 01, 2020	Apr. 30, 2020	Apr. 15, 2020	Apr. 07, 2020	Mar. 31, 2020	Mar. 31, 2019
Distributions
Cash distribution						$ 8	$ 13
Partnership's share of distributions						$ 65	$ 56
Northern Border
Distributions
Ownership interest						50.00%
Great Lakes
Distributions
Ownership interest						46.45%
Subsequent Events
Distributions
Cash distribution		$ 47
Subsequent Events | Two Percent interest
Distributions
Cash distribution, general partner		1
Subsequent Events | Northern Border
Distributions
Ownership interest			50.00%
Partnership's share of distributions			$ 8
Subsequent Events | Great Lakes
Distributions
Ownership interest			46.45%
Partnership's share of distributions			$ 21
Subsequent Events | Northern Border
Distributions
Limited partners, distribution declared					$ 16
Subsequent Events | Great Lakes
Distributions
Limited partners, distribution declared				$ 46
Subsequent Events | Iroquois
Distributions
Limited partners, distribution declared		$ 21
Subsequent Events | PNGTS
Distributions
Limited partners, distribution declared					$ 16
Share of distributions to its non-controlling interest owner			$ 6
Common Units | Subsequent Events
Distributions
Distribution declared (in dollars per unit)		$ 0.65
Cash distribution		$ 46
Common Units | General Partner | Subsequent Events
Distributions
Cash distribution		$ 4
Number of units held by investor		5,797,106
Common Units | TC Energy | Subsequent Events
Distributions
Cash distribution		$ 7
Number of units held by investor		11,287,725
Forecast | Iroquois
Distributions
Ownership interest	49.34%
Partnership's share of distributions	$ 11