TC Pipelines (TCP) 10-Q 3 Aug 17 2017 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2017	Aug. 01, 2017
Document and Entity Information
Entity Registrant Name	TC PIPELINES LP
Entity Central Index Key	1,075,607
Document Type	10-Q
Document Period End Date	Jun. 30, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		69,388,212
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q2

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016		Jun. 30, 2017		Jun. 30, 2016
Transmission revenues	$ 101	$ 101	[1]	$ 213		$ 212	[1]
Equity earnings (Note 4)	24	20	[1]	60		53	[1]
Operation and maintenance expenses	(17)	(14)	[1]	(31)		(25)	[1]
Property taxes	(7)	(7)	[1]	(14)		(14)	[1]
General and administrative	(2)	(2)	[1]	(4)		(4)	[1]
Depreciation	(25)	(24)	[1]	(49)		(48)	[1]
Financial charges and other (Note 14)	(19)	(17)	[1]	(36)		(35)	[1]
Net income before taxes	55	57	[1]	139		139	[1]
Income taxes (Note 18)				(1)		(1)	[1]
Net income	55	57	[1]	138	[2]	138	[1]
Net income attributable to non-controlling interests		2	[1]	6		8	[1]
Net income attributable to controlling interests	55	55	[1]	132		130	[1]
Net income attributable to controlling interest allocation (Note 8)
General Partner	5	3	[1]	8		5	[1]
TransCanada and its subsidiaries		2	[1]	2		4	[1]
Net income attributable to controlling interests	55	55	[1]	132		130	[1]
Common Units
Net income attributable to controlling interest allocation (Note 8)
Limited partners	$ 50	$ 50	[1]	$ 122		$ 121	[1]
Net income per common unit (Note 8) - basic (in dollars per unit)	$ 0.73	$ 0.76	[1],[3]	$ 1.78		$ 1.86	[1],[3]
Net income per common unit (Note 8) - diluted (in dollars per unit)	$ 0.73	$ 0.76		$ 1.78		$ 1.86
Weighted average common units outstanding - basic (in units)	68.9	65.5	[1]	68.6		64.9	[1]
Weighted average common units outstanding - diluted (in units)	68.9	65.5		68.6		64.9
Common units outstanding, end of period (in units)	69	65.9	[1]	69		65.9	[1]
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).
[2]	Recast to consolidate PNGTS for all periods presented. See Notes 2 and 6.
[3]	Net income per common unit prior to recast (Refer to Note 2).

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	[1]	Jun. 30, 2017		Jun. 30, 2016
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Net income	$ 55	$ 57		$ 138	[2]	$ 138	[1]
Other comprehensive income
Change in fair value of cash flow hedges (Note 12)		(1)		1		(3)
Amortization of realized loss on derivative financial instruments (Note 12)	1	1		1		1	[1]
Reclassification to net income of gains and losses on cash flow hedges (Note 12)	(1)			(1)
Comprehensive income	55	57		139		136
Comprehensive income attributable to non-controlling interests		2		6		8
Comprehensive income attributable to controlling interests	$ 55	$ 55		$ 133		$ 128
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).
[2]	Recast to consolidate PNGTS for all periods presented. See Notes 2 and 6.

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions		Jun. 30, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents		$ 51	$ 64	[1]
Accounts receivable and other (Note 13)		37	47	[1]
Inventories		7	7	[1]
Other		5	7	[1]
Total current assets		100	125	[1]
Equity investments (Note 4)		1,138	918	[1]
Plant, property and equipment (Net of $1,135 accumulated depreciation; 2016 - $1,088)		2,148	2,180	[1]
Goodwill		130	130	[1]
Other assets	[1]		1
Total assets		3,516	3,354	[1]
Current Liabilities
Accounts payable and accrued liabilities		27	29	[1]
Accounts payable to affiliates (Note 6 and 11)		35	8	[1]
Distribution payable	[1]		3
Accrued interest		11	10	[1]
Current portion of long-term debt (Note 5)		57	52	[1]
Total current liabilities		130	102	[1]
Long-term debt, net (Note 5)		2,333	1,859	[1]
Deferred state income taxes (Note 18)		10	10	[1]
Other liabilities		28	28	[1]
Total liabilities		2,501	1,999	[1]
Common units subject to rescission (Note 7)	[1]		83
Partners' Equity
General partner		25	27	[1]
Accumulated other comprehensive loss		(1)	(2)	[1]
Controlling interests		914	1,144	[1]
Non-controlling interests		101	97	[1]
Equity of former parent of PNGTS	[1]		31
Total partners' equity	[2]	1,015	1,272	[1]
Total liabilities and partners' equity		3,516	3,354	[1]
Common Units
Partners' Equity
Limited partner		795	1,002	[1]
Class B Units
Partners' Equity
Limited partner		$ 95	$ 117	[1]
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).
[2]	Recast to consolidate PNGTS for all periods presented. See Notes 2 and 6.

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2017	Jun. 30, 2016
CONSOLIDATED BALANCE SHEETS
Accumulated depreciation	$ 1,135	$ 1,088

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016
Cash Generated From Operations
Net income		$ 138	$ 138	[1]
Depreciation		49	48	[1]
Amortization of debt issue costs reported as interest expense		1	1	[1]
Amortization of realized loss on derivative instrument		(1)	(1)	[1]
Accrual for costs related to the 2017 Acquisition		1
Deferred state income tax recovery (Note 18)	[1]		(7)
Equity earnings from equity investments (Note 3 and 4)		(60)	(53)	[1]
Distributions received from operating activities of equity investments (Note 3)		68	95	[1]
Change in operating working capital (Note 10)		7	12	[1]
Net Cash Provided by (Used in) Operating Activities		205	235	[1]
Investing Activities
Capital expenditures		(16)	(18)	[1]
Other	[1]		2
Net Cash Provided by (Used in) Investing Activities		(625)	(213)	[1]
Financing Activities
Distributions paid to non-controlling interests		(5)	(9)	[1]
Common unit issuance, net (Note 7)		92
Common unit issuance subject to rescission, net (Note 7)	[1]		83
Long-term debt issued, net of discount (Note 5)		607	205	[1]
Long-term debt repaid (Note 5)		(128)	(165)	[1]
Debt issuance costs		(1)
Total financing activities		407	(25)	[1]
Decrease in cash and cash equivalents		(13)	(3)	[1]
Cash and cash equivalents, beginning of period	[1]	64	55
Cash and cash equivalents, end of period		51	52	[1]
Class B Units
Financing Activities
Distributions paid (Note 7)		(22)	(12)	[1]
Common units and General Partner interest combined
Financing Activities
Distributions paid (Note 9)		(135)	(119)	[1]
Great Lakes
Cash Generated From Operations
Equity earnings from equity investments (Note 3 and 4)		(23)	(19)
Investing Activities
Investment/Acquisition of interests		(4)	(4)	[1]
Portland Natural Gas Transmission System
Investing Activities
Investment/Acquisition of interests	[1]		(193)
Financing Activities
Distributions paid to former parent of PNGTS		(1)	$ (8)	[1]
Portland Natural Gas Transmission System And Iroquois Acquisition
Investing Activities
Investment/Acquisition of interests		$ (605)
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).

CONSOLIDATED STATEMENTS OF CAS7

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical)	Jun. 30, 2017	Jun. 01, 2017	Jun. 30, 2016
Portland Natural Gas Transmission System
Interest acquired (as a percent)	11.81%	11.81%	49.90%
Iroquois
Interest acquired (as a percent)	49.34%	49.34%

CONSOLIDATED STATEMENT OF CHANG

CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY - 6 months ended Jun. 30, 2017 - USD ($) shares in Millions, $ in Millions		Limited PartnersCommon Units	Limited PartnersClass B Units	General Partner	Accumulated Other Comprehensive Loss	[1]	Non-Controlling Interest		Equity of former parent of PNGTS		Total
Partners' Equity at beginning of year at Dec. 31, 2016		$ 1,002	$ 117	$ 27	$ (2)	[2]	$ 97	[2]	$ 31	[2]	$ 1,272	[2],[3]
Partners' Equity at beginning of year (in units) at Dec. 31, 2016		67.4	1.9
Increase (Decrease) in Partners' Equity
Net income	[2]	$ 122		8			6		2		138
Other comprehensive income	[2]				1						1
ATM equity issuance, net (Note 7)		$ 90		2							92	[2]
ATM equity issuance, net (Note 7) (in units)		1.6
Reclassification of common units no longer subject to rescission (Note 7 )		$ 81		2							83	[2]
Acquisition of interest in PNGTS and Iroquois (Note 6)		(371)		(8)					(32)	[2]	(411)	[2]
Distributions	[2]	(129)	$ (22)	(6)			(2)		$ (1)		(160)
Partners' Equity at end of year at Jun. 30, 2017		$ 795	$ 95	$ 25	$ (1)	[2]	$ 101	[2]			$ 1,015	[2]
Partners' Equity at end of year (in units) at Jun. 30, 2017		69	1.9
[1]	Losses related to cash flow hedges reported in Accumulated Other Comprehensive Loss and expected to be reclassified to Net Income in the next 12 months are estimated to be $2 million. These estimates assume constant interest rates over time; however, the amounts reclassified will vary based on actual value of interest rates at the date of settlement.Recast to consolidate PNGTS for all periods presented. See Notes 2 and 6.
[2]	Recast to consolidate PNGTS for all periods presented. See Notes 2 and 6.
[3]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).

CONSOLIDATED STATEMENT OF CHAN9

CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY (Parenthetical) $ in Millions	6 Months Ended
	Jun. 30, 2017USD ($)
CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY
Income expected to be reclassified to Net Income in the next 12 months	$ 2

ORGANIZATION

ORGANIZATION	6 Months Ended
	Jun. 30, 2017
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 (TransCanada Corporation together with its subsidiaries collectively referred to herein as TransCanada), to acquire, own and participate in the management of energy infrastructure assets in North America. The Partnership owns its pipeline assets through three intermediate limited partnerships (ILPs), TC GL Intermediate Limited Partnership, TC PipeLines Intermediate Limited Partnership and TC Tuscarora Intermediate Limited Partnership.

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES	6 Months Ended
	Jun. 30, 2017
SIGNIFICANT ACCOUNTING POLICIES
SIGNIFICANT ACCOUNTING POLICIES	NOTE 2 SIGNIFICANT ACCOUNTING POLICIES The accompanying financial statements and related notes have been prepared in accordance with United States generally accepted accounting principles (GAAP) and amounts are stated in U.S. dollars. The results of operations for the three and six months ended June 30, 2017 and 2016 are not necessarily indicative of the results that may be expected for the full fiscal year. The accompanying financial statements should be read in conjunction with the audited financial statements and notes thereto for the year ended December 31, 2016 included as exhibit 99.2 in our Current Report on Form 8-K dated August 3, 2017. That report contains a more comprehensive summary of the Partnership’s significant accounting policies. In the opinion of management, the accompanying financial statements contain all of the appropriate adjustments, all of which are normally recurring adjustments unless otherwise noted, and considered necessary to present fairly the financial position of the Partnership, the results of operations and cash flows for the respective periods. Our significant accounting policies are consistent with those disclosed in our audited financial statements and notes thereto for the year ended December 31, 2016 included as exhibit 99.2 in our Current Report on Form 8-K dated August 3, 2017, 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 in 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 TransCanada are considered common control transactions. When businesses are acquired from TransCanada that will be consolidated by the Partnership, the historical financial statements are required to be recast, except net income per common unit, to include the acquired entities for all periods presented. When the Partnership acquires an asset or an investment from TransCanada, 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. On June 1, 2017, the Partnership acquired from a subsidiary of TransCanada an additional 11.81 percent interest in PNGTS, resulting in the Partnership owning 61.71 percent in PNGTS (Refer to Note 6-Acquisitions). As a result of the Partnership owning 61.71 percent of PNGTS, the Partnership’s historical financial information has been recast, except net income (loss) per common unit, to consolidate PNGTS for all the periods presented in the Partnership’s consolidated financial statements. Additionally, this acquisition was accounted for as transaction between entities under common control, similar to pooling of interests, whereby the assets and liabilities of PNGTS were recorded at TransCanada’s carrying value. Also, on June 1, 2017, the Partnership acquired from subsidiaries of TransCanada a 49.34 percent interest in Iroquois Gas Transmission, L.P. (“Iroquois”) (Refer to Note 6-Acquisitions). Accordingly, this transaction was accounted for as a transaction between entities under common control, similar to pooling of interest, whereby the equity investment in Iroquois was recorded at TransCanada’s carrying value and was accounted for prospectively. Use of Estimates The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Although management believes these estimates are reasonable, actual results could differ from these estimates.

ACCOUNTING PRONOUNCEMENTS

ACCOUNTING PRONOUNCEMENTS	6 Months Ended
	Jun. 30, 2017
ACCOUNTING PRONOUNCEMENTS
ACCOUNTING PRONOUNCEMENTS	NOTE 3 ACCOUNTING PRONOUNCEMENTS Retrospective application of ASU No 2016-15 “ Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments” In August 2016, the FASB issued an amendment of previously issued guidance, which intends to reduce diversity in practice in how certain transactions are classified in the statement of cash flows. The new guidance is effective January 1, 2018, however, as early adoption is permitted, the Partnership elected to retrospectively apply this guidance effective December 31, 2016. The Partnership has elected to classify distributions received from equity method investees using the nature of distributions approach as it is more representative of the nature of the underlying activities of the investees that generated the distributions. As a result, certain comparative period distributions received from equity method investees, amounting to $42 million for the six months ended June 30, 2016, have been reclassified from investing activities to cash generated from operations in the consolidated statement of cash flows. Effective January 1, 2017 Inventory In July 2015, the FASB issued new guidance on simplifying the measurement of inventory. The new guidance specifies that an entity should measure inventory within the scope of this update at the lower of cost and net realizable value. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. This new guidance was effective January 1, 2017, and was applied prospectively and did not have a material impact on the Partnership’s consolidated balance sheet. Equity method and joint ventures In March 2016, the FASB issued new guidance that simplifies the transition to equity method accounting. The new guidance eliminates the requirement to retroactively apply the equity method of accounting when an increase in ownership interest in an investment qualifies for equity method accounting. The new guidance is effective January 1, 2017 and was applied prospectively. The application of this guidance did not have a material impact on the Partnership’s consolidated financial statements. Consolidation In October 2016, the FASB issued new guidance on consolidation relating to interests held through related parties that are under common control. The new guidance amends the consolidation requirements such that if a decision maker is required to evaluate whether it is the primary beneficiary of a variable interest entry (VIE), it will need to consider only its proportionate indirect interest in the VIE held through a common control party. The guidance was effective January 1, 2017, was applied retrospectively and did not result in any change to our consolidation conclusions. Future accounting changes Revenue from contracts with customers In 2014, the FASB issued new guidance on revenue from contracts with customers. The new guidance requires that an entity recognize revenue in accordance with a five-step model. This model is used to depict the transfer of promised goods or services to customers in an amount that reflects the total consideration to which it expects to be entitled to during the term of the contract in exchange for those goods or services. The new guidance also requires additional disclosures about the nature, amount, timing and uncertainty of revenue and the related cash flows. The Partnership will adopt the new standard on the effective date of January 1, 2018. There are two methods in which the new standard can be adopted: (1) a full retrospective approach with restatement of all prior periods presented, or (2) a modified retrospective approach with a cumulative-effect adjustment as of the date of adoption. The Partnership currently anticipates adopting the standard using the modified retrospective approach with the cumulative-effect of initially applying the guidance recognized at the date of adoption, subject to allowable and elected practical expedients. The Partnership has identified all existing customer contracts that are within the scope of the new guidance and is in the process of analyzing individual contracts or groups of contracts on a segmented basis to identify any significant changes in how revenues are recognized as a result of implementing the new standard. While the Partnership has not identified any material differences in the amount and timing of revenue recognition for the contracts that have been analyzed to date, the evaluation is not complete and the Partnership has not concluded on the overall impact of adopting the new guidance. The Partnership continues its segmented contract analysis to obtain the information necessary to quantify, the cumulative-effect adjustment, if any, on prior period revenues. The Partnership also continues to address any system and process changes necessary to compile the information to meet the recognition and disclosure requirements of the new guidance. Leases In February 2016, the FASB issued new guidance on the accounting for leases. The new guidance amends the definition of a lease requiring the customer 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 in order for the arrangement to qualify as a lease. The new guidance also establishes a right-of-use model (ROU) that requires a lessee to recognize a ROU asset and corresponding lease liability on the balance sheet for all leases with a term longer than 12 months. Leases will be classified as finance or operating, with classification affecting the pattern and classification of expense recognition in the income statement. The new guidance does not make extensive changes to lessor accounting. The new guidance is effective on January 1, 2019, with early adoption permitted. A modified retrospective transition approach is required for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements, with certain practical expedients available. The Partnership is continuing to identify and analyze existing lease agreements to determine the effect of adoption of the new guidance on its consolidated financial statements. The Partnership is also addressing system and process changes necessary to compile the information to meet the recognition and disclosure requirements of the new guidance. Goodwill Impairment In January 2017, the FASB issued new guidance on simplifying the test for goodwill impairment by eliminating the requirement to calculate the implied fair value of goodwill to measure the impairment charge. Instead, entities will record an impairment charge based on the excess of a reporting unit’s carrying amount over its fair value. This new guidance is effective January 1, 2020 and will be applied prospectively. Early adoption is permitted. The Partnership is currently evaluating the impact of the adoption of this guidance and has not yet determined the effect on its consolidated financial statements.

EQUITY INVESTMENTS

EQUITY INVESTMENTS	6 Months Ended
	Jun. 30, 2017
EQUITY INVESTMENTS
EQUITY INVESTMENTS	NOTE 4 EQUITY INVESTMENTS The Partnership has equity interests in Northern Border, Great Lakes and effective June 1, 2017, 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 TransCanada. 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 17). Ownership Equity Earnings Equity Investments Interest at Three months Six Months (unaudited) June 30, ended June 30, ended June 30, June 30, December 31, (millions of dollars) 2017 2017 2016 (b) 2017 2016 (b) 2017 2016 (b) Northern Border (a) % Great Lakes % Iroquois % — — — (a) Equity earnings from Northern Border is net of the 12-year amortization of a $10 million transaction fee paid to the operator of Northern Border at the time of the Partnership’s acquisition of an additional 20 percent interest in April 2006. (b) Recast to eliminate equity earnings from PNGTS and consolidate PNGTS for all periods presented (Refer to Note 2). Northern Border The Partnership did not have undistributed earnings from Northern Border for the three and six months ended June 30, 2017 and 2016. The summarized financial information for Northern Border is as follows: (unaudited) (millions of dollars) June 30, 2017 December 31, 2016 ASSETS Cash and cash equivalents Other current assets Plant, property and equipment, net Other assets LIABILITIES AND PARTNERS’ EQUITY Current liabilities Deferred credits and other Long-term debt, including current maturities, net Partners’ equity Partners’ capital Accumulated other comprehensive loss ) ) Three months ended Six months ended (unaudited) June 30, June 30, (millions of dollars) 2017 2016 2017 2016 Transmission revenues Operating expenses ) ) ) ) Depreciation ) ) ) ) Financial charges and other ) ) ) ) Net income Great Lakes The Partnership made an equity contribution to Great Lakes of $4 million in the first quarter of 2017. This amount represents the Partnership’s 46.45 percent share of a $9 million cash call from Great Lakes to make a scheduled debt repayment. The Partnership did not have undistributed earnings from Great Lakes for the three and six months ended June 30, 2017 and 2016. The summarized financial information for Great Lakes is as follows: (unaudited) (millions of dollars) June 30, 2017 December 31, 2016 ASSETS Current assets Plant, property and equipment, net LIABILITIES AND PARTNERS’ EQUITY Current liabilities Long-term debt, including current maturities, net Partners’ equity Three months ended Six months ended (unaudited) June 30, June 30, (millions of dollars) 2017 2016 2017 2016 Transmission revenues Operating expenses ) ) ) ) Depreciation ) ) ) ) Financial charges and other ) ) ) ) Net income Iroquois On June 1, 2017, the Partnership acquired a 49.34 percent interest in Iroquois (Refer to Note 6). The Partnership recorded no undistributed earnings from Iroquois in June 2017. The summarized financial information for Iroquois is as follows: (unaudited) (millions of dollars) June 30, 2017 December 31, 2016 ASSETS Cash and cash equivalents Other current assets Plant, property and equipment, net Other assets LIABILITIES AND PARTNERS’ EQUITY Current liabilities Long-term debt, including current maturities, net Other non-current liabilities Partners’ equity Three months ended Six months ended (unaudited) June 30, June 30, (millions of dollars) 2017 2016 2017 2016 Transmission revenues Operating expenses ) ) ) ) Depreciation ) ) ) ) Financial charges and other ) ) ) ) Net income

DEBT AND CREDIT FACILITIES

DEBT AND CREDIT FACILITIES	6 Months Ended
	Jun. 30, 2017
DEBT AND CREDIT FACILITIES
DEBT AND CREDIT FACILITIES	NOTE 5 DEBT AND CREDIT FACILITIES (unaudited) June 30, Weighted Average December 31, (a) Weighted Average (b) TC PipeLines, LP Senior Credit Facility due 2021 % % 2013 Term Loan Facility due July 2018 % % 2015 Term Loan Facility due September 2018 % % 4.65% Unsecured Senior Notes due 2021 % (b) % (b) 4.375% Unsecured Senior Notes due 2025 % (b) % (b) 3.90 % Unsecured Senior Notes due 2027 % (b) — — GTN 5.29% Unsecured Senior Notes due 2020 % (b) % (b) 5.69% Unsecured Senior Notes due 2035 % (b) % (b) Unsecured Term Loan Facility due 2019 % % PNGTS 5.90% Senior Secured Notes due December 2018 % (b) % (b) Tuscarora Unsecured Term Loan due 2019 % % 3.82% Series D Senior Notes due 2017 % (b) % (b) Less: unamortized debt issuance costs and debt discount Less: current portion (a) Recast as discussed in Notes 2 and 6. (b) 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, under which $170 million was outstanding at June 30, 2017 (December 31, 2016 - $160 million), leaving $330 million available for future borrowing. The LIBOR-based interest rate on the Senior Credit Facility was 2.34 percent at June 30, 2017 (December 31, 2016 — 1.92 percent). As of June 30, 2017, the variable interest rate exposure related to the 2013 Term Loan Facility was hedged by fixed interest rate swap arrangements and our effective interest rate was 2.31 percent (December 31, 2016 — 2.31 percent). Prior to hedging activities, the LIBOR-based interest rate on the 2013 Term Loan Facility was 2.31 percent at June 30, 2017 (December 31, 2016 — 1.87 percent). The LIBOR-based interest rate on the 2015 Term Loan Facility was 2.20 percent at June 30, 2017 (December 31, 2016 — 1.77 percent). The 2013 Term Loan Facility and the 2015 Term Loan Facility (Term Loan Facilities) and the Senior Credit Facility require the Partnership to maintain a certain leverage ratio (debt to adjusted cash flow [net income plus cash distributions received, extraordinary losses, interest expense, expense for taxes paid or accrued, and depreciation and amortization expense less equity earnings and extraordinary gains]) no greater than 5.00 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 4.60 to 1.00 as of June 30, 2017. On May 25, 2017, the Partnership closed a $500 million public offering of senior unsecured notes bearing an interest rate of 3.90 percent maturing May 25, 2027. The net proceeds of $497 million were used to fund a portion of the 2017 Acquisition (Refer to Note 6).The indenture for the notes contains customary investment grade covenants. PNGTS PNGTS’ Senior Secured Notes are secured by the PNGTS long-term firm shipper contracts and its partners’ pledge of their equity and a guarantee of debt service for six months. PNGTS is restricted under the terms of its note purchase agreement from making cash distributions unless certain conditions are met. Before a distribution can be made, the debt service reserve account must be fully funded and PNGTS’ debt service coverage ratio for the preceding and succeeding twelve months must be 1.30 or greater. At June 30, 2017, the debt service coverage ratio was 1.82 for the twelve preceding months and 2.99 for the twelve succeeding months. Therefore, PNGTS was not restricted to make any cash distributions. 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 June 30, 2017 was 44.3 percent. The LIBOR-based interest rate on the GTN’s Unsecured Term Loan Facility was 2.00 percent at June 30, 2017 (December 31, 2016 — 1.57 percent). Tuscarora Tuscarora’s Series D Senior Notes, which require yearly principal payments until maturity, are secured by Tuscarora’s transportation contracts, supporting agreements and substantially all of Tuscarora’s property. The note purchase agreements contain certain provisions that include, among other items, limitations on additional indebtedness and distributions to partners. The Series D Senior Notes contain a covenant that limits total debt to no greater than 45 percent of Tuscarora’s total capitalization. Tuscarora’s total debt to total capitalization ratio at June 30, 2017 was 20.46 percent. Additionally, the Series D Senior Notes require Tuscarora to maintain a Debt Service Coverage Ratio (cash available from operations divided by a sum of interest expense and principal payments) of greater than 3.00 to 1.00. The ratio was 3.12 to 1.00 as of June 30, 2017. The LIBOR-based interest rate on the Tuscarora’s Unsecured Term Loan Facility was 2.36 percent at June 30, 2017 (December 31, 2016 — 1.90 percent). At June 30, 2017, the Partnership was in compliance with its financial covenants, in addition to the other covenants which include restrictions on entering into mergers, consolidations and sales of assets, granting liens, material amendments to the Third Amended and Restated Agreement of Limited Partnership (Partnership Agreement), incurring additional debt and distributions to unitholders. The principal repayments required of the Partnership on its debt are as follows: (unaudited) (millions of dollars) 2017 2018 2019 2020 2021 Thereafter

ACQUISITION

ACQUISITION	6 Months Ended
	Jun. 30, 2017
ACQUISITION
ACQUISITION	NOTE 6 ACQUISITION 2017 Acquisition On June 1, 2017, the Partnership acquired from subsidiaries of TransCanada a 49.34 percent interest in Iroquois Gas Transmission System, L.P. (Iroquois), including an option to acquire a further 0.66 percent interest in Iroquois, together with an additional 11.81 percent interest in PNGTS resulting in the Partnership owning a 61.71 percent interest in PNGTS (2017 Acquisition). The total purchase price of the 2017 Acquisition was $765 million plus preliminary purchase price adjustments amounting to $9 million. The purchase price consisted of (i) $710 million for the Iroquois interest (less $164 million, which reflected our 49.34 percent share of Iroquois outstanding debt on June 1) (ii) $55 million for the additional 11.81 percent interest in PNGTS (less $5 million, which reflected our 11.81% proportionate share in PNGTS’ debt on June 1) and (iii) preliminary working capital adjustments on PNGTS and Iroquois amounting to $3 million and $6 million, respectively. Additionally, the Partnership paid $1,000 for the option to acquire TransCanada’s remaining 0.66 percent interest in Iroquois. The Partnership funded the cash portion of the 2017 Acquisition through a combination of proceeds from the May 2017 public debt offering (refer to Note 5) and borrowing under our Senior Credit Facility. As at the date of the 2017 Acquisition, there was significant cash on Iroquois’ balance sheet. Pursuant to the Purchase and Sale Agreement associated with the acquisition of the Iroquois interest, as amended, the Partnership agreed to pay $28 million plus interest to TransCanada on August 1, 2017 for its 49.34 percent share of cash determined to be surplus to Iroquois’ operating needs. In addition, the Partnership expects to make a final working capital adjustment payment by the end of August. The $28 million and the related interest were included in accounts payable to affiliates at June 30, 2017. The Iroquois’ partners adopted a distribution resolution to address the significant cash on Iroquois’ balance sheet post-closing. The Partnership expects to receive the $28 million of unrestricted cash as part of its quarterly distributions from Iroquois over 11 quarters under the terms of the resolution, beginning with the second quarter 2017 distribution on August 1, 2017. The acquisition of a 49.34 percent interest in Iroquois was accounted for as a transaction between entities under common control, whereby the equity investment in Iroquois was recorded at TransCanada’s carrying value and the total excess purchase price paid was recorded as a reduction in Partners’ Equity. Iroquois’ net purchase price was allocated as follows: (millions of dollars) Net Purchase Price (a) Less: TransCanada’s carrying value of Iroquois at June 1, 2017 Excess purchase price (b) (a) Total purchase price of $710 million plus the additional consideration on Iroquois surplus cash amounting to approximately $29 million including interest less the assumption of $164 million of proportional Iroquois debt by the Partnership. (b) The excess purchase price of $358 million was recorded as a reduction in Partners’ Equity. The acquisition of an additional 11.81 percent interest in PNGTS, which resulted in the Partnership owning 61.71 percent in PNGTS, was accounted for as a transaction between entities under common control, similar to a pooling of interests, whereby assets and liabilities of PNGTS were recorded at TransCanada’s carrying value and the Partnership’s historical financial information, except net income per common unit, was recast to consolidate PNGTS for all periods presented. The PNGTS purchase price was recorded as follows: (millions of dollars) Current assets Property, plant and equipment, net Current liabilities ) Deferred state income taxes ) Long-term debt, including current portion ) Non-controlling interest ) Carrying value of pre-existing Investment in PNGTS ) TransCanada’s carrying value of the acquired 11.81 percent interest at June 1, 2017 Excess purchase price over net assets acquired (b) Total cash consideration (a) (a) Total purchase price of $58 million (including preliminary working capital adjustment) less the assumption of $5 million of proportional PNGTS debt by the Partnership. (b) The excess purchase price of $21 million was recorded as a reduction in Partners’ Equity.

PARTNERS' EQUITY

PARTNERS' EQUITY	6 Months Ended
	Jun. 30, 2017
PARTNERS' EQUITY
PARTNERS' EQUITY	NOTE 7 PARTNERS’ EQUITY ATM equity issuance program (ATM program) During the six months ended June 30, 2017, we issued 1,542,921 common units under our ATM program generating net proceeds of approximately $90 million, plus $2 million from the General Partner to maintain its effective two percent general partner interest. The commissions to our sales agents in the six months ended June 30, 2017 were approximately $1 million. The net proceeds were used for general partnership purposes. Class B units issued to TransCanada The Class B Units we issued on April 1, 2015 to finance a portion of the 2015 GTN Acquisition represent a limited partner interest in us and entitle TransCanada to an annual distribution based on 30 percent of GTN’s annual distributions as follows: (i) 100 percent of distributions above $20 million through March 31, 2020; and (ii) 25 percent of distributions above $20 million thereafter. For the year ending December 31, 2017, the Class B units’ equity account will be increased by the excess of 30 percent of GTN’s distributions over the annual threshold of $20 million until such amount is declared for distribution and paid in the first quarter of 2018. During the six months ended June 30, 2017, the threshold has not been exceeded. For the year ended December 31, 2016, the Class B distribution was $22 million and was declared and paid in the first quarter of 2017. Common unit issuance subject to rescission In connection with a late filing of an employee-related Form 8-K with the SEC in March 2016, the Partnership became ineligible to use the then effective shelf registration statement upon filing of its 2015 Annual Report. As a result, it was determined that the purchasers of the 1.6 million common units that were issued from March 8, 2016 to May 19, 2016 under the Partnership’s ATM program may have had a rescission right for an amount equal to the purchase price paid for the units, plus statutory interest and less any distributions paid, upon the return of such units to the Partnership. The Securities Act generally requires that any claim brought for a violation of Section 5 of the Securities Act be brought within one year of violation. At December 31, 2016, $83 million was recorded as Common units subject to rescission on the consolidated balance sheet. The Partnership classified all the 1.6 million common units sold under its ATM program from March 8, 2016 up to and including May 19, 2016, which may be subject to rescission rights, outside of equity given the potential redemption feature which is not within the control of the Partnership. These units were treated as outstanding for financial reporting purposes. No unitholder claimed or attempted to exercise any rescission rights prior to their expiry dates and the final rights related to the sales of such units expired on May 19, 2017. Therefore, all the common units subject to rescission were reclassified back to partners’ equity on our consolidated balance sheet at June 30, 2017.

NET INCOME PER COMMON UNIT

NET INCOME PER COMMON UNIT	6 Months Ended
	Jun. 30, 2017
NET INCOME PER COMMON UNIT
NET INCOME PER COMMON UNIT	NOTE 8 NET INCOME PER COMMON UNIT Net income per common unit is computed by dividing net income attributable to controlling interests, after deduction of net income attributed to PNGTS’ former parent, amounts attributable to the General Partner and Class B units, by the weighted average number of common units outstanding. The amounts allocable to the General Partner equals an amount based upon the General Partner’s effective two percent general partner interest, plus an amount equal to incentive distributions. Incentive distributions are paid to the General Partner if quarterly cash distributions on the common units exceed levels specified in the Partnership Agreement. The amount allocable to the Class B units in 2017 equals 30 percent of GTN’s distributable cash flow during the year ended December 31, 2017 less $20 million (December 31, 2016 —$20 million). Net income per common unit was determined as follows: Three months ended Six months ended (unaudited) June 30, June 30, (millions of dollars, except per common unit amounts) 2017 2016 (a) 2017 2016 (a) Net income attributable to controlling interests (a) Net income attributable to PNGTS’ former parent (a) (b) — ) ) ) Net income attributable to General and Limited Partners Incentive distributions allocated to the General Partner (c) ) ) ) ) Net income attributable to the Class B units (d) — ) — ) Net income attributable to the General Partner and common units Net income attributable to General Partner’s two percent interest ) ) ) ) Net income attributable to common units Weighted average common units outstanding (millions) — basic and diluted (e ) (e ) Net income per common unit — basic and diluted $ $ (f ) $ $ (f) (a) Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6). (b) Net income allocable to General and Limited Partners excludes net income attributed to PNGTS’ former parent as it was allocated to TransCanada and was not allocable to either the general partner, common units or Class B units. (c) Under the terms of the Partnership Agreement, for any quarterly period, the participation of the incentive distribution rights (IDRs) is limited to the available cash distributions declared. Accordingly, incentive distributions allocated to the General Partner are based on the Partnership’s available cash during the current reporting period, but declared and paid in the subsequent reporting period. (d) During the three and six months ended June 30, 2017, no amounts were allocated to the Class B units as the annual threshold of $20 million has not been exceeded. During the six months ended June 30, 2016, 30 percent of GTN’s total distributable cash flow was $21 million. As a result of exceeding the $20 million threshold, $1 million of net income attributable to controlling interests was allocated to the Class B units during the three and six months ended June 30, 2016. (e) Includes the common units subject to rescission. These units are treated as outstanding for financial reporting purposes. Refer to Note 7. (f) Net income per common unit prior to recast (Refer to Note 2).

CASH DISTRIBUTIONS

CASH DISTRIBUTIONS	6 Months Ended
	Jun. 30, 2017
CASH DISTRIBUTIONS
CASH DISTRIBUTIONS	NOTE 9 CASH DISTRIBUTIONS During the three and six months ended June 30, 2017, the Partnership distributed $0.94 and $1.88 per common unit, respectively (June 30, 2016 — $0.89 and $1.78 per common unit) for a total of $68 million and $135 million, respectively (June 30, 2016 - $60 million and $119 million). The distribution paid to our General Partner during the three months ended June 30, 2017 for its effective two percent general partner interest was $1 million along with an IDR payment of $2 million for a total distribution of $3 million (June 30, 2016 - $1 million for the effective two percent interest and a $1 million IDR payment). The distribution paid to our General Partner during the six months ended June 30, 2017 for its effective two percent general partner interest was $2 million along with an IDR payment of $4 million for a total distribution of $6 million (June 30, 2016 - $2 million for the effective two percent interest and a $2 million IDR payment).

CHANGE IN OPERATING WORKING CAP

CHANGE IN OPERATING WORKING CAPITAL	6 Months Ended
	Jun. 30, 2017
CHANGE IN OPERATING WORKING CAPITAL
CHANGE IN OPERATING WORKING CAPITAL	NOTE 10 CHANGE IN OPERATING WORKING CAPITAL (unaudited) Six months ended June 30, (millions of dollars) 2017 2016 (a) Change in accounts receivable and other Change in other current assets Change in accounts payable and accrued liabilities (b) ) Change in accounts payable to affiliates ) ) Change in state income taxes payable — Change in accrued interest Change in operating working capital (a) Recast as discussed in Notes 2 and 6. (b) The accrual of $10 million for the construction of GTN’s Carty Lateral in December 31, 2015 was paid during the first quarter 2016. Accordingly, the payment was reported as capital expenditures in our cash flow statement during the current period.

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS	6 Months Ended
	Jun. 30, 2017
RELATED PARTY TRANSACTIONS
RELATED PARTY TRANSACTIONS	NOTE 11 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 the conduct of the business of, and allocable to, the Partnership. Such costs include (i) overhead costs (such as office space and equipment) and (ii) out-of-pocket expenses related to the provision of such services. The Partnership Agreement provides that the General Partner will determine the costs that are allocable to the Partnership in any reasonable manner determined by the General Partner in its sole discretion. For both the three and six months ended June 30, 2017 and 2016, total costs charged to the Partnership by the General Partner were $1 million and $2 million, respectively. As operator of our pipelines except Iroquois, TransCanada’s subsidiaries provide capital and operating services to our pipeline systems. TransCanada’s subsidiaries incur costs on behalf of our pipeline systems, including, but not limited to, employee salary and benefit costs, and property and liability insurance costs. The Iroquois pipeline system is operated by Iroquois Pipeline Operating Company, a wholly owned subsidiary of Iroquois. Therefore, Iroquois does not receive any capital and operating services from TransCanada. Capital and operating costs charged to our pipeline systems for the three and six months ended June 30, 2017 and 2016 by TransCanada’s subsidiaries and amounts payable to TransCanada’s subsidiaries at June 30, 2017 and December 31, 2016 are summarized in the following tables: Three months ended Six months ended (unaudited) June 30, June 30, (millions of dollars) 2017 2016 2017 2016 Capital and operating costs charged by TransCanada’s subsidiaries to: Great Lakes (a) Northern Border (a) GTN Bison — North Baja Tuscarora PNGTS Impact on the Partnership’s net income: Great Lakes (a) Northern Border (a) GTN Bison North Baja Tuscarora PNGTS (b) (unaudited) (millions of dollars) June 30, 2017 December 31, 2016 Net amounts payable to TransCanada’s subsidiaries is as follows: Great Lakes (a) Northern Border (a) GTN Bison North Baja — Tuscarora — PNGTS (a) Represents 100 percent of the costs. (b) Recast to consolidate PNGTS for all periods presented (Refer to Note 2). Great Lakes earns significant transportation revenues from TransCanada and its affiliates, some of which are provided at discounted rates and some at maximum recourse rates. For the three and six months ended June 30, 2017, Great Lakes earned 43 percent and 57 percent of transportation revenues from TransCanada and its affiliates, respectively (June 30, 2016 — 64 percent and 71 percent). At June 30, 2017, $1 million was included in Great Lakes’ receivables in regards to the transportation contracts with TransCanada and its affiliates (December 31, 2016 — $19 million). Great Lakes operates under a FERC approved 2013 rate settlement that includes a revenue sharing mechanism that requires Great Lakes to share with its shippers certain percentages of any qualifying revenues earned above a certain return on equity threshold. For the year ended December 31, 2016, Great Lakes recorded an estimated 2016 revenue sharing provision of $7.2 million. For the three and six months ended June 30, 2017, Great Lakes recorded an estimated 2017 revenue sharing provision of $7 million and $10 million, respectively. Great Lakes expects that a significant percentage of this refund will be paid to its affiliates. PNGTS earns transportation revenues from TransCanada and its affiliates. For the three and six months ended June 30, 2017, PNGTS earned 2 percent and 1 percent of transportation revenues from TransCanada and its affiliates, respectively (June 30, 2016 — 5 percent and 3 percent). At June 30, 2017, nil was included in PNGTS’ receivables in regards to the transportation contracts with TransCanada and its affiliates (December 31, 2016 — nil).

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	6 Months Ended
	Jun. 30, 2017
FAIR VALUE MEASUREMENTS
FAIR VALUE MEASUREMENTS	NOTE 12 FAIR VALUE MEASUREMENTS (a) Fair Value Hierarchy Under ASC 820, Fair Value Measurements and Disclosures , fair value measurements are characterized in one of three levels based upon the inputs used to arrive at the measurement. The three levels of the fair value hierarchy are as follows: · Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that we have the ability to access at the measurement date. · Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. · Level 3 inputs are unobservable inputs for the asset or liability. When appropriate, valuations are adjusted for various factors including credit considerations. Such adjustments are generally based on available market evidence. In the absence of such evidence, management’s best estimate is used. (b) Fair Value of Financial Instruments The carrying value of cash and cash equivalents, accounts receivable and other, accounts payable and accrued liabilities, accounts payable to affiliates and accrued interest approximate their fair values because of the short maturity or duration of these instruments, or because the instruments bear a variable rate of interest or a rate that approximates current rates. The fair value of the Partnership’s debt is estimated by discounting the future cash flows of each instrument at estimated current borrowing rates. The fair value of interest rate derivatives is calculated using the income approach, which uses period-end market rates and applies a discounted cash flow valuation model. Long-term debt is recorded at amortized cost and classified in Level 2 of the fair value hierarchy for fair value disclosure purposes. Interest rate derivative assets and liabilities are classified in Level 2 for all periods presented where the fair value is determined by using valuation techniques that refer to observable market data or estimated market prices. The estimated fair value of the Partnership’s debt as at June 30, 2017 and December 31, 2016 was $2,465 million and $1,908 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 interest rate derivatives to manage its exposure to interest rate risk. We regularly assess the impact of interest rate fluctuations on future cash flows and evaluate hedging opportunities to mitigate our interest rate risk. The interest rate swaps are structured such that the cash flows of the derivative instruments match those of the variable rate of interest on the 2013 Term Loan Facility. The Partnership hedged interest payments on the variable-rate 2013 Term Loan Facility with interest rate swaps maturing July 1, 2018, at a weighted average fixed interest rate of 2.31 percent. At June 30, 2017, the fair value of the interest rate swaps accounted for as cash flow hedges was an asset of $2 million (both on a gross and net basis). At December 31, 2016, the fair value of the interest rate swaps accounted for as cash flow hedges was an asset of $1 million and a liability of $1 million (on a gross basis) and an asset of nil million (on a net basis). The Partnership did not record any amounts in net income related to ineffectiveness for interest rate hedges for the three and six months ended June 30, 2017 and 2016. The change in fair value of interest rate derivative instruments recognized in other comprehensive income was nil and a gain of $1 million for the three and six months ended June 30, 2017, respectively (June 30, 2016 — loss of $1 million and a loss of $3 million). For the three and six months ended June 30, 2017, the net realized loss related to the interest rate swaps was nil, and was included in financial charges and other (June 30, 2016 —$1 million for both periods). Refer to Note 14 — Financial Charges and Other. In anticipation of a debt refinancing in 2003, PNGTS entered into forward interest rate swap agreements to hedge the interest rate on its Senior Secured Notes due in 2018. These interest rate swaps were used to manage the impact of interest rate fluctuations and qualified as derivative financial instruments in accordance with ASC 815, Derivatives and Hedging . PNGTS settled its position with a payment of $20.9 million to counterparties at the time of the refinancing and recorded the realized loss in accumulated other comprehensive income as of the termination date. The previously recorded loss is currently being amortized against earnings over the life of the PNGTS Senior Secured Notes. At June 30, 2017, our 61.71 percent proportionate share of net unamortized loss on PNGTS included in other comprehensive income was $1 million (December 31, 2016 - $2 million). For the three and six months ended June 30, 2017, our 61.71 percent proportionate share of the amortization of realized loss on derivative instruments was $1 million (June 30, 2016 —$1 million). The Partnership has no master netting agreements; however, it has derivative contracts containing provisions with rights of offset. The Partnership has elected to present the fair value of derivative instruments with the right to offset on a gross basis in the balance sheet. Had the Partnership elected to present these instruments on a net basis, there would be no effect on the consolidated balance sheet as of June 30, 2017 (net asset of nil million as of December 31, 2016).

ACCOUNTS RECEIVABLE AND OTHER

ACCOUNTS RECEIVABLE AND OTHER	6 Months Ended
	Jun. 30, 2017
ACCOUNTS RECEIVABLE AND OTHER
ACCOUNTS RECEIVABLE AND OTHER	NOTE 13 ACCOUNTS RECEIVABLE AND OTHER (unaudited) (millions of dollars) June 30, 2017 December 31, 2016 (a) Trade accounts receivable, net of allowance of nil Imbalance receivable from affiliates Other (a) Recast as discussed in Notes 2 and 6.

FINANCIAL CHARGES AND OTHER

FINANCIAL CHARGES AND OTHER	6 Months Ended
	Jun. 30, 2017
FINANCIAL CHARGES AND OTHER
FINANCIAL CHARGES AND OTHER	NOTE 14 FINANCIAL CHARGES AND OTHER Three months ended Six months ended (unaudited) June 30, June 30, (millions of dollars) 2017 2016 (b) 2017 2016 (b) Interest Expense (a) PNGTS’ amortization of derivative loss on derivative instruments (Note 12) (b) Net realized loss related to the interest rate swaps — — Other Income ) ) ) ) (a) Includes amortization of debt issuance costs and discount costs. (b) Recast to consolidate PNGTS for all periods presented (Refer to Note 2).

CONTINGENCIES

CONTINGENCIES	6 Months Ended
	Jun. 30, 2017
CONTINGENCIES
CONTINGENCIES	NOTE 15 CONTINGENCIES Great Lakes v. Essar Steel Minnesota LLC, et al . — On October 29, 2009, Great Lakes filed suit in the U.S. District Court, District of Minnesota, against Essar Minnesota LLC (Essar Minnesota) and certain Foreign Essar Affiliates (collectively, Essar) for breach of its monthly payment obligation under its transportation services agreement with Great Lakes. Great Lakes sought to recover approximately $33 million for past and future payments due under the agreement. On September 16, 2015, following a jury trial, the federal district court judge entered a judgment in the amount of $32.9 million in favor of Great Lakes. On September 20, 2015, Essar appealed the decision to the United States Court of Appeals for the Eighth Circuit (Eighth Circuit) based on an allegation of improper jurisdiction and a number of other rulings by the federal district judge. Essar was required to post a performance bond for the full value of the judgment pending appeal. In July 2016, Essar Minnesota filed for Bankruptcy. The performance bond was released into the bankruptcy court proceedings. The Foreign Essar Affiliates have not filed for bankruptcy. The Eighth Circuit heard the appeal on October 20, 2016. A decision on the appeal was received in December 2016 and the Eighth Circuit vacated Great Lakes’ judgment against Essar finding that there was no federal jurisdiction. Great Lakes filed a Request for Rehearing with the Eighth Circuit and it was denied in January 2017. Great Lakes currently is proceeding against Essar Minnesota in the bankruptcy court and its case against the Foreign Essar Affiliates in Minnesota state court remains pending. In April, after reaching agreement with creditors on an allowed claim, the Bankruptcy court approved Great Lakes’ claim in the amount of $31.5 million.

REGULATORY

REGULATORY	6 Months Ended
	Jun. 30, 2017
REGULATORY
REGULATORY	NOTE 16 REGULATORY North Baja — On January 6, 2017, North Baja notified FERC that current market conditions do not support the replacement of the compression that was temporarily abandoned in 2013 and requested authorization to permanently abandon two compressor units and a nominal volume of unsubscribed firm capacity. FERC approved the permanent abandonment request on February 16, 2017. The abandonments will not have any impact on existing firm transportation service. Great Lakes- Great Lakes is required to file a new section 4 rate case with rates effective no later than January 1, 2018 as part of the settlement agreement with customers approved in November 2013. On March 31, 2017, Great Lakes filed its rate case pursuant to Section 4 of the Natural Gas Act (2017 Rate Case). The rates proposed in the filing will become effective on October 1, 2017, subject to refund, if alternate resolution to the proceeding is not reached prior to that date. Great Lakes has initiated customer discussions regarding the details of the filing and is currently seeking to achieve a mutually beneficial resolution through settlement with its customers.

VARIABLE INTEREST ENTITIES

VARIABLE INTEREST ENTITIES	6 Months Ended
	Jun. 30, 2017
VARIABLE INTEREST ENTITIES
VARIABLE INTEREST ENTITIES	NOTE 17 VARIABLE INTEREST ENTITIES In the normal course of business, the Partnership must re-evaluate its legal entities under the 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 variable interest entity (VIE) is a legal entity that does not have sufficient equity at risk to finance its activities without additional subordinated financial support or is structured such that equity investors lack the ability to make significant decisions relating to the entity’s operations through voting rights or do not substantively participate in the gains or losses of the entity. A VIE is appropriately consolidated if the Partnership is considered to be the primary beneficiary. The VIE’s primary beneficiary is the entity that has both (1) the power to direct the activities of the VIE that most significantly impact the VIEs economic performance and (2) the obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE. As a result of its analysis, the Partnership continues to consolidate all legal entities in which it has a variable interest and for which it is considered to be the primary beneficiary. VIEs where the Partnership is not the primary beneficiary, but has a variable interest in the entity, are accounted for as equity investments. Consolidated VIEs The Partnership’s consolidated VIEs consist of the Partnership’s ILPs that hold interests in the Partnership’s pipeline systems. After considering the purpose and design of the ILPs and the risks that they were designed to create and pass through to the Partnership, the Partnership has concluded that it is the primary beneficiary of these ILPs because of the significant amount of variability that it absorbs from the ILPs’ economic performance. The assets and liabilities held through these VIEs that are not available to creditors of the Partnership and whose investors have no recourse to the credit of the Partnership are held through GTN, Tuscarora, Northern Border, Great Lakes, PNGTS and Iroquois 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) June 30, 2017 December 31, 2016 (a) ASSETS (LIABILITIES) * Cash and cash equivalents Accounts receivable and other Inventories Other current assets Equity investments Plant, property and equipment Other assets Accounts payable and accrued liabilities ) ) Accounts payable to affiliates, net ) ) Distributions payable — ) Accrued interest ) ) Current portion of long-term debt ) ) Long-term debt ) ) Other liabilities ) ) Deferred state income tax ) ) *North Baja and Bison, which are also assets held through our consolidated VIEs, are excluded as the assets of these entities can be used for purposes other than the settlement of the VIE’s obligations. (a) Recast to consolidate PNGTS for all periods presented (Refer to Note 2).

INCOME TAXES

INCOME TAXES	6 Months Ended
	Jun. 30, 2017
INCOME TAXES
INCOME TAXES	NOTE 18 INCOME TAXES The Partnership’s income taxes relate to business profits tax (BPT) levied at the partnership (PNGTS) level by the state of New Hampshire. As a result of the BPT, PNGTS recognizes deferred taxes related to temporary differences between the financial statement carrying amount of existing assets and liabilities and their respective tax bases. The deferred taxes at June 30, 2017 and December 31, 2016 relate primarily to utility plant. At June 30, 2017 and December 31, 2016 the New Hampshire BPT effective tax rate was 3.8 percent for both periods and was applied to PNGTS’ taxable income. Three months ended Six months ended (unaudited) June 30, June 30, (millions of dollars) 2017 2016 (a) 2017 2016 (a) State income taxes Current — — Deferred — — — ) — — (a) Recast to consolidate PNGTS for all periods presented (Refer to Note 2).

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	6 Months Ended
	Jun. 30, 2017
SUBSEQUENT EVENTS.
SUBSEQUENT EVENTS	NOTE 19 SUBSEQUENT EVENTS Management of the Partnership has reviewed subsequent events through August 3, 2017, the date the financial statements were issued, and concluded there were no events or transactions during this period that would require recognition or disclosure in the consolidated financial statements other than what is disclosed here and/or those already disclosed in the preceding notes. On July 20, 2017, the board of directors of the General Partner declared the Partnership’s second quarter 2017 cash distribution in the amount of $1.00 per common unit payable on August 11, 2017 to unitholders of record as of August 1, 2017. The declared distribution reflects a $0.06 per common unit increase to the Partnership’s first quarter 2017 quarterly distribution. The declared distribution totaled $74 million and is payable in the following manner: $69 million to common unitholders (including $6 million to the General Partner as a holder of 5,797,106 common units and $11 million to another subsidiary of TransCanada as holder of 11,287,725 common units) and $5 million to the General Partner, which included $2 million for its effective two percent general partner interest and $3 million in respect of its IDRs. Northern Border declared its June 2017 distribution of $14 million on July 7, 2017, of which the Partnership will receive its 50 percent share or $7 million on July 31, 2017. Great Lakes declared its second quarter 2017 distribution of 15 million on July 18, 2017, of which the Partnership will receive its 46.45 percent share or $7 million on August 1, 2017. Iroquois declared its second quarter 2017 distribution of $28 million on July 27, 2017, of which the Partnership received its 49.34 percent share or $14 million on August 1, 2017.

SIGNIFICANT ACCOUNTING POLICI29

SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
	Jun. 30, 2017
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 in 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 TransCanada are considered common control transactions. When businesses are acquired from TransCanada that will be consolidated by the Partnership, the historical financial statements are required to be recast, except net income per common unit, to include the acquired entities for all periods presented. When the Partnership acquires an asset or an investment from TransCanada, 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. On June 1, 2017, the Partnership acquired from a subsidiary of TransCanada an additional 11.81 percent interest in PNGTS, resulting in the Partnership owning 61.71 percent in PNGTS (Refer to Note 6-Acquisitions). As a result of the Partnership owning 61.71 percent of PNGTS, the Partnership’s historical financial information has been recast, except net income (loss) per common unit, to consolidate PNGTS for all the periods presented in the Partnership’s consolidated financial statements. Additionally, this acquisition was accounted for as transaction between entities under common control, similar to pooling of interests, whereby the assets and liabilities of PNGTS were recorded at TransCanada’s carrying value. Also, on June 1, 2017, the Partnership acquired from subsidiaries of TransCanada a 49.34 percent interest in Iroquois Gas Transmission, L.P. (“Iroquois”) (Refer to Note 6-Acquisitions). Accordingly, this transaction was accounted for as a transaction between entities under common control, similar to pooling of interest, whereby the equity investment in Iroquois was recorded at TransCanada’s carrying value and was accounted for prospectively.
Use of Estimates	Use of Estimates The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Although management believes these estimates are reasonable, actual results could differ from these estimates.

EQUITY INVESTMENTS (Tables)

EQUITY INVESTMENTS (Tables)	6 Months Ended
	Jun. 30, 2017
EQUITY INVESTMENTS
Schedule of equity investments and summarized financial information for equity investees	Ownership Equity Earnings Equity Investments Interest at Three months Six Months (unaudited) June 30, ended June 30, ended June 30, June 30, December 31, (millions of dollars) 2017 2017 2016 (b) 2017 2016 (b) 2017 2016 (b) Northern Border (a) % Great Lakes % Iroquois % — — — (a) Equity earnings from Northern Border is net of the 12-year amortization of a $10 million transaction fee paid to the operator of Northern Border at the time of the Partnership’s acquisition of an additional 20 percent interest in April 2006. (b) Recast to eliminate equity earnings from PNGTS and consolidate PNGTS for all periods presented (Refer to Note 2).
Northern Border
EQUITY INVESTMENTS
Schedule of equity investments and summarized financial information for equity investees	(unaudited) (millions of dollars) June 30, 2017 December 31, 2016 ASSETS Cash and cash equivalents Other current assets Plant, property and equipment, net Other assets LIABILITIES AND PARTNERS’ EQUITY Current liabilities Deferred credits and other Long-term debt, including current maturities, net Partners’ equity Partners’ capital Accumulated other comprehensive loss ) ) Three months ended Six months ended (unaudited) June 30, June 30, (millions of dollars) 2017 2016 2017 2016 Transmission revenues Operating expenses ) ) ) ) Depreciation ) ) ) ) Financial charges and other ) ) ) ) Net income
Great Lakes
EQUITY INVESTMENTS
Schedule of equity investments and summarized financial information for equity investees	(unaudited) (millions of dollars) June 30, 2017 December 31, 2016 ASSETS Current assets Plant, property and equipment, net LIABILITIES AND PARTNERS’ EQUITY Current liabilities Long-term debt, including current maturities, net Partners’ equity Three months ended Six months ended (unaudited) June 30, June 30, (millions of dollars) 2017 2016 2017 2016 Transmission revenues Operating expenses ) ) ) ) Depreciation ) ) ) ) Financial charges and other ) ) ) ) Net income
Iroquois
EQUITY INVESTMENTS
Schedule of equity investments and summarized financial information for equity investees	(unaudited) (millions of dollars) June 30, 2017 December 31, 2016 ASSETS Cash and cash equivalents Other current assets Plant, property and equipment, net Other assets LIABILITIES AND PARTNERS’ EQUITY Current liabilities Long-term debt, including current maturities, net Other non-current liabilities Partners’ equity Three months ended Six months ended (unaudited) June 30, June 30, (millions of dollars) 2017 2016 2017 2016 Transmission revenues Operating expenses ) ) ) ) Depreciation ) ) ) ) Financial charges and other ) ) ) ) Net income

DEBT AND CREDIT FACILITIES (Tab

DEBT AND CREDIT FACILITIES (Tables)	6 Months Ended
	Jun. 30, 2017
DEBT AND CREDIT FACILITIES
Schedule of debt and credit facilities	(unaudited) June 30, Weighted Average December 31, (a) Weighted Average (b) TC PipeLines, LP Senior Credit Facility due 2021 % % 2013 Term Loan Facility due July 2018 % % 2015 Term Loan Facility due September 2018 % % 4.65% Unsecured Senior Notes due 2021 % (b) % (b) 4.375% Unsecured Senior Notes due 2025 % (b) % (b) 3.90 % Unsecured Senior Notes due 2027 % (b) — — GTN 5.29% Unsecured Senior Notes due 2020 % (b) % (b) 5.69% Unsecured Senior Notes due 2035 % (b) % (b) Unsecured Term Loan Facility due 2019 % % PNGTS 5.90% Senior Secured Notes due December 2018 % (b) % (b) Tuscarora Unsecured Term Loan due 2019 % % 3.82% Series D Senior Notes due 2017 % (b) % (b) Less: unamortized debt issuance costs and debt discount Less: current portion (a) Recast as discussed in Notes 2 and 6. (b) Fixed interest rate
Schedule of principal repayments required on debt	(unaudited) (millions of dollars) 2017 2018 2019 2020 2021 Thereafter

ACQUISITION (Tables)

ACQUISITION (Tables)	6 Months Ended
	Jun. 30, 2017
ACQUISITION
Schedule of net purchase price	(millions of dollars) Net Purchase Price (a) Less: TransCanada’s carrying value of Iroquois at June 1, 2017 Excess purchase price (b) (a) Total purchase price of $710 million plus the additional consideration on Iroquois surplus cash amounting to approximately $29 million including interest less the assumption of $164 million of proportional Iroquois debt by the Partnership. (b) The excess purchase price of $358 million was recorded as a reduction in Partners’ Equity.
Schedule of purchase price allocation	(millions of dollars) Current assets Property, plant and equipment, net Current liabilities ) Deferred state income taxes ) Long-term debt, including current portion ) Non-controlling interest ) Carrying value of pre-existing Investment in PNGTS ) TransCanada’s carrying value of the acquired 11.81 percent interest at June 1, 2017 Excess purchase price over net assets acquired (b) Total cash consideration (a) (a) Total purchase price of $58 million (including preliminary working capital adjustment) less the assumption of $5 million of proportional PNGTS debt by the Partnership. (b) The excess purchase price of $21 million was recorded as a reduction in Partners’ Equity.

NET INCOME PER COMMON UNIT (Tab

NET INCOME PER COMMON UNIT (Tables)	6 Months Ended
	Jun. 30, 2017
NET INCOME PER COMMON UNIT
Schedule of net income per common unit	Three months ended Six months ended (unaudited) June 30, June 30, (millions of dollars, except per common unit amounts) 2017 2016 (a) 2017 2016 (a) Net income attributable to controlling interests (a) Net income attributable to PNGTS’ former parent (a) (b) — ) ) ) Net income attributable to General and Limited Partners Incentive distributions allocated to the General Partner (c) ) ) ) ) Net income attributable to the Class B units (d) — ) — ) Net income attributable to the General Partner and common units Net income attributable to General Partner’s two percent interest ) ) ) ) Net income attributable to common units Weighted average common units outstanding (millions) — basic and diluted (e ) (e ) Net income per common unit — basic and diluted $ $ (f ) $ $ (f) (a) Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6). (b) Net income allocable to General and Limited Partners excludes net income attributed to PNGTS’ former parent as it was allocated to TransCanada and was not allocable to either the general partner, common units or Class B units. (c) Under the terms of the Partnership Agreement, for any quarterly period, the participation of the incentive distribution rights (IDRs) is limited to the available cash distributions declared. Accordingly, incentive distributions allocated to the General Partner are based on the Partnership’s available cash during the current reporting period, but declared and paid in the subsequent reporting period. (d) During the three and six months ended June 30, 2017, no amounts were allocated to the Class B units as the annual threshold of $20 million has not been exceeded. During the six months ended June 30, 2016, 30 percent of GTN’s total distributable cash flow was $21 million. As a result of exceeding the $20 million threshold, $1 million of net income attributable to controlling interests was allocated to the Class B units during the three and six months ended June 30, 2016. (e) Includes the common units subject to rescission. These units are treated as outstanding for financial reporting purposes. Refer to Note 7. (f) Net income per common unit prior to recast (Refer to Note 2).

CHANGE IN OPERATING WORKING C34

CHANGE IN OPERATING WORKING CAPITAL (Tables)	6 Months Ended
	Jun. 30, 2017
CHANGE IN OPERATING WORKING CAPITAL
Schedule of change in operating working capital	(unaudited) Six months ended June 30, (millions of dollars) 2017 2016 (a) Change in accounts receivable and other Change in other current assets Change in accounts payable and accrued liabilities (b) ) Change in accounts payable to affiliates ) ) Change in state income taxes payable — Change in accrued interest Change in operating working capital (a) Recast as discussed in Notes 2 and 6. (b) The accrual of $10 million for the construction of GTN’s Carty Lateral in December 31, 2015 was paid during the first quarter 2016. Accordingly, the payment was reported as capital expenditures in our cash flow statement during the current period.

RELATED PARTY TRANSACTIONS (Tab

RELATED PARTY TRANSACTIONS (Tables)	6 Months Ended
	Jun. 30, 2017
RELATED PARTY TRANSACTIONS
Summary of capital and operating costs charged to pipeline systems by related party	Three months ended Six months ended (unaudited) June 30, June 30, (millions of dollars) 2017 2016 2017 2016 Capital and operating costs charged by TransCanada’s subsidiaries to: Great Lakes (a) Northern Border (a) GTN Bison — North Baja Tuscarora PNGTS Impact on the Partnership’s net income: Great Lakes (a) Northern Border (a) GTN Bison North Baja Tuscarora PNGTS (b)
Summary of amount payable to related party for costs charged	(unaudited) (millions of dollars) June 30, 2017 December 31, 2016 Net amounts payable to TransCanada’s subsidiaries is as follows: Great Lakes (a) Northern Border (a) GTN Bison North Baja — Tuscarora — PNGTS (a) Represents 100 percent of the costs. (b) Recast to consolidate PNGTS for all periods presented (Refer to Note 2).

ACCOUNTS RECEIVABLE AND OTHER (

ACCOUNTS RECEIVABLE AND OTHER (Tables)	6 Months Ended
	Jun. 30, 2017
ACCOUNTS RECEIVABLE AND OTHER
Schedule of accounts receivable and other	(unaudited) (millions of dollars) June 30, 2017 December 31, 2016 (a) Trade accounts receivable, net of allowance of nil Imbalance receivable from affiliates Other (a) Recast as discussed in Notes 2 and 6.

FINANCIAL CHARGES AND OTHER (Ta

FINANCIAL CHARGES AND OTHER (Tables)	6 Months Ended
	Jun. 30, 2017
FINANCIAL CHARGES AND OTHER
Schedule of components of financial charges and other	Three months ended Six months ended (unaudited) June 30, June 30, (millions of dollars) 2017 2016 (b) 2017 2016 (b) Interest Expense (a) PNGTS’ amortization of derivative loss on derivative instruments (Note 12) (b) Net realized loss related to the interest rate swaps — — Other Income ) ) ) ) (a) Includes amortization of debt issuance costs and discount costs. (b) Recast to consolidate PNGTS for all periods presented (Refer to Note 2).

VARIABLE INTEREST ENTITIES (Tab

VARIABLE INTEREST ENTITIES (Tables)	6 Months Ended
	Jun. 30, 2017
VARIABLE INTEREST ENTITIES
Schedule of assets and liabilities held through VIEs whose assets cannot be used for purposes other settlement of their obligations	(unaudited) June 30, 2017 December 31, 2016 (a) ASSETS (LIABILITIES) * Cash and cash equivalents Accounts receivable and other Inventories Other current assets Equity investments Plant, property and equipment Other assets Accounts payable and accrued liabilities ) ) Accounts payable to affiliates, net ) ) Distributions payable — ) Accrued interest ) ) Current portion of long-term debt ) ) Long-term debt ) ) Other liabilities ) ) Deferred state income tax ) ) *North Baja and Bison, which are also assets held through our consolidated VIEs, are excluded as the assets of these entities can be used for purposes other than the settlement of the VIE’s obligations. (a) Recast to consolidate PNGTS for all periods presented (Refer to Note 2).

INCOME TAXES (Tables)

INCOME TAXES (Tables)	6 Months Ended
	Jun. 30, 2017
INCOME TAXES
Schedule of state income taxes of PNGTS	Three months ended Six months ended (unaudited) June 30, June 30, (millions of dollars) 2017 2016 (a) 2017 2016 (a) State income taxes Current — — Deferred — — — ) — — (a) Recast to consolidate PNGTS for all periods presented (Refer to Note 2).

ORGANIZATION - Ownership Intere

ORGANIZATION - Ownership Interests in Natural Gas Pipeline Systems (Details)	6 Months Ended
	Jun. 30, 2017LimitedPartnership
ORGANIZATION
Number of intermediate limited partnerships through which pipeline assets are owned	3

SIGNIFICANT ACCOUNTING POLICI41

SIGNIFICANT ACCOUNTING POLICIES - Basis of Presentation (Details)	Jun. 30, 2017	Jun. 01, 2017	Jun. 30, 2016
Portland Natural Gas Transmission System
ACQUISITION
Ownership interest (as a percent)	11.81%	11.81%	49.90%
Iroquois
ACQUISITION
Ownership interest (as a percent)		49.34%
Portland Natural Gas Transmission System
ACQUISITION
Ownership interest (as a percent)		11.81%
Interest acquired by Partnership (as a percent)		61.71%

ACCOUNTING PRONOUNCEMENTS - Sta

ACCOUNTING PRONOUNCEMENTS - Statement of Cash Flows (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
ACCOUNTING PRONOUNCEMENTS
Distributions from equity investments	$ 68	$ 95	[1]
Adjustment | ASU 2016-15, Statement of Cash Flows
ACCOUNTING PRONOUNCEMENTS
Cumulative distributions in excess of equity earnings		(42)
Distributions from equity investments		$ 42
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).

EQUITY INVESTMENTS (Details)

EQUITY INVESTMENTS (Details) - USD ($) $ in Millions	Aug. 01, 2017	Jun. 01, 2017	Apr. 30, 2006	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016		Jun. 30, 2017	Jun. 30, 2016		Jul. 31, 2017	Dec. 31, 2016
EQUITY INVESTMENTS
Equity Earnings				$ 24		$ 20	[1]	$ 60	$ 53	[1]
Equity Investments				1,138		918		1,138	918			$ 918	[1]
LIABILITIES AND PARTNERS' EQUITY
Current portion of long-term debt				$ 57				57				52	[1]
Amount borrowed								607	205	[1]
Great Lakes
EQUITY INVESTMENTS
Total cash call issued to fund debt repayment								$ 9
Northern Border
EQUITY INVESTMENTS
Ownership interest (as a percent)				50.00%				50.00%			50.00%
Equity Earnings				$ 15		16		$ 34	34
Equity Investments				437		444		437	444
Amortization period of transaction fee			12 years
Transaction fee			$ 10
Additional ownership interest acquired (as a percent)			20.00%
Assets
Cash and cash equivalents				16				16				14
Other current assets				34				34				36
Plant, property and equipment, net				1,077				1,077				1,089
Other assets				14				14				14
Assets, total				1,141				1,141				1,153
LIABILITIES AND PARTNERS' EQUITY
Current liabilities				37				37				38
Deferred credits and other				30				30				28
Long-term debt, including current maturities, net				430				430				430
Partners' equity
Partners' equity				645				645				659
Accumulated other comprehensive loss				(1)				(1)				(2)
Liabilities and Partners' Equity, total				1,141				1,141				1,153
Revenues (expenses)
Transmission revenues				69		70		144	144
Operating expenses				(18)		(18)		(36)	(35)
Depreciation				(15)		(15)		(30)	(29)
Financial charges and other				(5)		(6)		(9)	(11)
Net income				$ 31		31		$ 69	69
Great Lakes
EQUITY INVESTMENTS
Ownership interest (as a percent)	46.45%			46.45%				46.45%
Equity Earnings				$ 6		4		$ 23	19
Equity Investments				475		474		475	474
Equity contribution					$ 4			4	4	[1]
Assets
Current assets				61				61				66
Plant, property and equipment, net				705				705				714
Assets, total				766				766				780
LIABILITIES AND PARTNERS' EQUITY
Current liabilities				34				34				40
Long-term debt, including current maturities, net				269				269				278
Partners' equity
Partners' equity				463				463				462
Liabilities and Partners' Equity, total				766				766				780
Revenues (expenses)
Transmission revenues				41		36		103	97
Operating expenses				(17)		(15)		(30)	(30)
Depreciation				(7)		(7)		(14)	(14)
Financial charges and other				(5)		(5)		(10)	(11)
Net income				$ 12		9		$ 49	42
Iroquois
EQUITY INVESTMENTS
Ownership interest (as a percent)		49.34%		49.34%				49.34%
Equity Earnings				$ 3				$ 3
Equity Investments				226				226
Undistributed earnings								0
Equity contribution	$ 28	$ 710
Assets
Cash and cash equivalents				100				100				88
Other current assets				26				26				27
Plant, property and equipment, net				595				595				611
Other assets				8				8				7
Assets, total				729				729				733
LIABILITIES AND PARTNERS' EQUITY
Current liabilities				15				15				16
Long-term debt, including current maturities, net				332				332				338
Other non-current liabilities				9				9				5
Partners' equity
Partners' equity				373				373				374
Liabilities and Partners' Equity, total				729				729				$ 733
Revenues (expenses)
Transmission revenues				45		47		98	100
Operating expenses				(13)		(15)		(29)	(30)
Depreciation				(7)		(10)		(14)	(19)
Financial charges and other				(5)		(4)		(9)	(8)
Net income				$ 20		$ 18		$ 46	$ 43
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).

DEBT AND CREDIT FACILITIES - Am

DEBT AND CREDIT FACILITIES - Amounts Outstanding and Description of Terms (Details)	May 25, 2017USD ($)	Jun. 30, 2017USD ($)entity	Dec. 31, 2016USD ($)
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities		$ 2,402,000,000	$ 1,920,000,000
Less: unamortized debt issuance costs and debt discount		12,000,000	9,000,000
Less: current portion		57,000,000	52,000,000	[1]
Long-term debt		$ 2,333,000,000	1,859,000,000	[1]
Senior Credit Facility due in 2021 and the Term Loan Facilities due in 2018
Credit facilities, short-term loan facility and long-term debt
Leverage ratio, actual (as a percent)		460.00%
Senior Credit Facility due in 2021 and the Term Loan Facilities due in 2018 | Debt agreement covenants, initial period after occurrence of acquisition
Credit facilities, short-term loan facility and long-term debt
Additional period immediately following the fiscal quarter in which a specified material acquisition occurs		6 months
Senior Credit Facility due in 2021 and the Term Loan Facilities due in 2018 | Debt agreement covenants, initial period after occurrence of acquisition | Minimum
Credit facilities, short-term loan facility and long-term debt
Number of acquisitions | entity		1
Senior Credit Facility due in 2021 and the Term Loan Facilities due in 2018 | Debt agreement covenants, initial period after occurrence of acquisition | Maximum
Credit facilities, short-term loan facility and long-term debt
Leverage ratio, covenant (as a percent)		550.00%
Senior Credit Facility due in 2021 and the Term Loan Facilities due in 2018 | Debt agreement covenants, periods subsequent to initial period after occurrence of acquisition | Maximum
Credit facilities, short-term loan facility and long-term debt
Leverage ratio, covenant (as a percent)		500.00%
Revolving credit facility | TC Pipelines, LP Senior Credit Facility due 2021
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities		$ 170,000,000	$ 160,000,000
Weighted Average Interest Rate (as a percent)		2.22%	1.72%
Maximum borrowing capacity		$ 500,000,000
Amount outstanding under credit facility		170,000,000	$ 160,000,000
Remaining borrowing capacity		$ 330,000,000
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)		2.34%	1.92%
Term loan | TC PipeLines, LP 2013 Term Loan Facility due July 2018
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities		$ 500,000,000	$ 500,000,000
Weighted Average Interest Rate (as a percent)		2.15%	1.73%
Term loan | TC PipeLines, LP 2013 Term Loan Facility due July 2018 | LIBOR borrowings | LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end (as a percent)		2.31%	1.87%
Term loan | TC PipeLines, LP 2013 Term Loan Facility due July 2018 | LIBOR borrowings | LIBOR | Hedges of cash flows | Interest rate swaps
Credit facilities, short-term loan facility and long-term debt
Weighted Average Interest Rate (as a percent)		2.31%	2.31%
Term loan | TC PipeLines, LP 2015 Term Loan Facility due September 2018
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities		$ 170,000,000	$ 170,000,000
Weighted Average Interest Rate (as a percent)		2.04%	1.63%
Term loan | TC PipeLines, LP 2015 Term Loan Facility due September 2018 | LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end (as a percent)		2.20%	1.77%
Unsecured debt | TC PipeLines, LP 4.65% Senior Notes due 2021
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)		4.65%	4.65%
Debt and credit facilities		$ 350,000,000	$ 350,000,000
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
Stated interest rate (as a percent)		4.375%	4.375%
Debt and credit facilities		$ 350,000,000	$ 350,000,000
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
Stated interest rate (as a percent)	3.90%	3.90%	3.90%
Debt and credit facilities		$ 500,000,000
Weighted Average Interest Rate (as a percent)		3.90%
Amount of debt	$ 500,000,000
Net proceeds	$ 497,000,000
Unsecured debt | GTN 5.29% Senior Notes due 2020
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)		5.29%	5.29%
Debt and credit facilities		$ 100,000,000	$ 100,000,000
Weighted Average Interest Rate (as a percent)		5.29%	5.29%
Unsecured debt | GTN 5.69% Senior Notes due 2035
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)		5.69%	5.69%
Debt and credit facilities		$ 150,000,000	$ 150,000,000
Weighted Average Interest Rate (as a percent)		5.69%	5.69%
Unsecured debt | GTN Term Loan Facility due 2019
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities		$ 55,000,000	$ 65,000,000
Weighted Average Interest Rate (as a percent)		1.84%	1.43%
Unsecured debt | Tuscarora Term Loan due 2019
Credit facilities, short-term loan facility and long-term debt
Debt and credit facilities		$ 9,000,000	$ 10,000,000
Weighted Average Interest Rate (as a percent)		2.03%	1.64%
Unsecured debt | Tuscarora Term Loan due 2019 | LIBOR
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end (as a percent)		236.00%	190.00%
Secured debt | PNGTS 5.90% Senior Secured Notes due December 2018
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)		5.90%	5.90%
Debt and credit facilities		$ 36,000,000	$ 53,000,000
Weighted Average Interest Rate (as a percent)		5.90%	5.90%
Secured debt | Tuscarora 3.82% Series D Senior Notes due 2017
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)		3.82%	3.82%
Debt and credit facilities		$ 12,000,000	$ 12,000,000
Weighted Average Interest Rate (as a percent)		3.82%	3.82%
Portland Natural Gas Transmission System | Secured debt | PNGTS 5.90% Senior Secured Notes due December 2018
Credit facilities, short-term loan facility and long-term debt
Debt Service, number of months of guarantee		6 months
Portland Natural Gas Transmission System | Secured debt | PNGTS 5.90% Senior Secured Notes due December 2018 | Debt agreement covenants, preceding twelve months
Credit facilities, short-term loan facility and long-term debt
Debt Service Coverage, Actual (as a percent)		182.00%
Portland Natural Gas Transmission System | Secured debt | PNGTS 5.90% Senior Secured Notes due December 2018 | Debt agreement covenants, preceding twelve months | Minimum
Credit facilities, short-term loan facility and long-term debt
Debt Service Coverage, covenant (as a percent)		130.00%
Portland Natural Gas Transmission System | Secured debt | PNGTS 5.90% Senior Secured Notes due December 2018 | Debt agreement covenants, succeeding twelve months
Credit facilities, short-term loan facility and long-term debt
Debt Service Coverage, Actual (as a percent)		299.00%
Portland Natural Gas Transmission System | Secured debt | PNGTS 5.90% Senior Secured Notes due December 2018 | Debt agreement covenants, succeeding twelve months | Minimum
Credit facilities, short-term loan facility and long-term debt
Debt Service Coverage, covenant (as a percent)		130.00%
GTN | Unsecured debt | Senior Notes and Term Loan Facility due 2019
Credit facilities, short-term loan facility and long-term debt
Debt interest rate, at period end (as a percent)		2.00%	1.57%
Percentage of debt to total capitalization, actual		44.30%
GTN | Unsecured debt | Senior Notes and Term Loan Facility due 2019 | Maximum
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization, covenant		70.00%
Tuscarora Gas Transmission Company | Unsecured debt | Tuscarora 3.82% Series D Senior Notes due 2017
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization, actual		20.46%
Debt Service Coverage, Actual (as a percent)		312.00%
Tuscarora Gas Transmission Company | Unsecured debt | Tuscarora 3.82% Series D Senior Notes due 2017 | Minimum
Credit facilities, short-term loan facility and long-term debt
Debt Service Coverage, covenant (as a percent)		300.00%
Tuscarora Gas Transmission Company | Unsecured debt | Tuscarora 3.82% Series D Senior Notes due 2017 | Maximum
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization, covenant		45.00%
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).

DEBT AND CREDIT FACILITIES - Pr

DEBT AND CREDIT FACILITIES - Principal Payments Required (Details) $ in Millions	Jun. 30, 2017USD ($)
Principal repayments required on debt
2,017	$ 24
2,018	715
2,019	43
2,020	100
2,021	520
Thereafter	1,000
Total debt	$ 2,402

ACQUISITION - 2017 Acquisition

ACQUISITION - 2017 Acquisition (Details)	Aug. 01, 2017USD ($)item	Jun. 01, 2017USD ($)	Jun. 30, 2017USD ($)
Iroquois
ACQUISITION
Interest acquired (as a percent)		49.34%	49.34%
Option to acquire (as a percent)		0.66
Preliminary purchase price adjustments		$ 6,000,000
Net purchase price	$ 28,000,000	710,000,000
Outstanding debt		164,000,000
Payment for option to acquire		1,000
Iroquois net purchase price
Net Purchase Price		581,000,000
Less: TransCanada's carrying value of Iroquois at June 1, 2017		223,000,000
Excess purchase price		358,000,000
Purchase price before assumption of debt		710,000,000
Reduction in partner's equity under equity method investments		$ 358,000,000
Iroquois | Accounts payable to affiliates
ACQUISITION
Net purchase price			$ 28,000,000
Portland Natural Gas Transmission System
ACQUISITION
Interest acquired (as a percent)		11.81%
Interest acquired by Partnership (as a percent)		61.71%
Preliminary purchase price adjustments		$ 3,000,000
Net purchase price		55,000,000
Outstanding debt		5,000,000
PNGTS purchase price
Current assets		25,000,000
Property, plant and equipment, net		294,000,000
Current liabilities		(4,000,000)
Deferred state income taxes		(10,000,000)
Long-term debt, including current portion		(41,000,000)
Net Purchase Price		264,000,000
Non-controlling interest		(100,000,000)
Carrying value of pre-existing Investment in PNGTS		(132,000,000)
TransCanada's carrying value of the acquired 11.81 percent interest at June 1, 2017		32,000,000
Excess purchase price over net assets acquired		21,000,000
Total cash consideration		53,000,000
Purchase price before assumption of debt		58,000,000
Reduction in partner's equity due to excess purchase price		21,000,000
Portland Natural Gas Transmission System | Iroquois
ACQUISITION
Purchase price		765,000,000
Preliminary purchase price adjustments		$ 9,000,000
Subsequent Events | Iroquois | Investing Activities
ACQUISITION
Return on investment distribution classified as investing activities	$ 28,000,000
Number of quarters for distribution of surplus cash | item	11

PARTNERS' EQUITY - ATM Equity I

PARTNERS' EQUITY - ATM Equity Issuance Program (Details) - USD ($)		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
PARTNERS' EQUITY
Net proceeds from issuance of common units	[1]			$ 92,000,000
General Partner
PARTNERS' EQUITY
Net proceeds from issuance of common units				$ 2,000,000
TC PipeLines GP, Inc. | General Partner
PARTNERS' EQUITY
Ownership interest in the Partnership (as a percent)		2.00%	2.00%	2.00%	2.00%
ATM Equity Issuance Program | Common Units
PARTNERS' EQUITY
Units sold				1,542,921
Net proceeds from issuance of common units				$ 90,000,000
Sales agent commissions				1
ATM Equity Issuance Program | TC PipeLines GP, Inc. | General Partner
PARTNERS' EQUITY
Equity contribution				$ 2,000,000
[1]	Recast to consolidate PNGTS for all periods presented. See Notes 2 and 6.

PARTNERS' EQUITY - Class B Unit

PARTNERS' EQUITY - Class B Units (Details) - Class B Units - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2017	Jun. 30, 2017	Jun. 30, 2016
PARTNERS' EQUITY
Limited Partners, Distributions paid	$ 22	$ 22	$ 12	[1]
GTN | TransCanada | 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 (as a percent)		30.00%
Percentage applied to 30 percent of GTN's distributions above threshold through March 31, 2020		100.00%
Threshold of GTN's total distributable cash flows for payment to Class B units		$ 20
Percentage applied to GTN's distributions above threshold after March 31, 2020		25.00%
Percentage applied to GTN's distributable cash flow for the twelve month period ending December 31, 2017		30.00%	30.00%
30% of GTN's distributable cash flow			$ 21
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).

PARTNERS' EQUITY - Reclassifica

PARTNERS' EQUITY - Reclassification of units (Details) - USD ($) shares in Millions, $ in Millions		2 Months Ended
		May 19, 2016	Dec. 31, 2016
PARTNERS' EQUITY
Common units subject to rescission	[1]		$ 83
ATM Equity Issuance Program | Common Units
PARTNERS' EQUITY
Reclassification of common unit issuance subject to rescission, net (in units)		1.6
Common units subject to rescission			$ 83
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).

NET INCOME PER COMMON UNIT - Ge

NET INCOME PER COMMON UNIT - General Partner Effective Interest and Allocated Incentive Distributions (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
TC PipeLines GP, Inc. | General Partner
PARTNERS' EQUITY
General partner interest (as a percent)	2.00%	2.00%	2.00%	2.00%

NET INCOME PER COMMON UNIT - Te

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			6 Months Ended			12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016		Jun. 30, 2017	Jun. 30, 2016		Dec. 31, 2016
Net income (loss) per common unit
Net income attributable to controlling interests	$ 55	$ 55	[1]	$ 132	$ 130	[1]
Net income attributable to PNGTS' former parent		(1)		(2)	(3)
Net income attributable to General and Limited Partners	55	54		130	127
Incentive distributions allocated to the General Partner	(3)	(2)		(5)	(3)
Net income attributable to the General Partner and common units	52	51		125	123
Net income attributable to General Partner's two percent interest	(2)	(1)		(3)	(2)
Class B Units
Net income (loss) per common unit
Net income attributable to limited partners		(1)			(1)
Common Units
Net income (loss) per common unit
Net income attributable to limited partners	$ 50	$ 50	[1]	$ 122	$ 121	[1]
Weighted average common units outstanding - basic (in units)	68.9	65.5	[1]	68.6	64.9	[1]
Weighted average common units outstanding - diluted (in units)	68.9	65.5		68.6	64.9
Net income per common unit - basic (in dollars per unit)	$ 0.73	$ 0.76	[1],[2]	$ 1.78	$ 1.86	[1],[2]
Net income per common unit - diluted (in dollars per unit)	$ 0.73	$ 0.76		$ 1.78	$ 1.86
GTN | Class B Units | TransCanada | Distributions
Net income (loss) per common unit
Net income attributable to controlling interests	$ 0	$ 1		$ 0	$ 1
Distributions
Percentage applied to GTN's distributable cash flow for the twelve month period ending December 31, 2017				30.00%	30.00%
Threshold of GTN's distributions for payment to Class B units	$ 20	$ 20		$ 20	$ 20		$ 20
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%
30% of GTN's distributable cash flow					$ 21
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).
[2]	Net income per common unit prior to recast (Refer to Note 2).

CASH DISTRIBUTIONS - Distributi

CASH DISTRIBUTIONS - Distributions Paid (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Common Units
Distributions
Per Unit Distribution, paid (in dollars per unit)	$ 0.94	$ 0.89	$ 1.88	$ 1.78
Total cash distribution	$ 68	$ 60	$ 135	$ 119
Common units and General Partner interest combined
Distributions
Total distribution of general partner interest and IDR payment	3		6
TC PipeLines GP, Inc. | General Partner
Distributions
Total distribution for General Partner interest	$ 1	$ 1	$ 2	$ 2
General partner interest (as a percent)	2.00%	2.00%	2.00%	2.00%
TC PipeLines GP, Inc. | Common units and General Partner interest combined
Distributions
Incentive distribution paid to the General Partner	$ 2	$ 1	$ 4	$ 2

CHANGE IN OPERATING WORKING C53

CHANGE IN OPERATING WORKING CAPITAL - Components (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
CHANGE IN OPERATING WORKING CAPITAL
Change in accounts receivable and other	$ 11	$ 2
Change in other current assets	2	2
Change in accounts payable and accrued liabilities	(5)	1
Change in accounts payable to affiliates	(2)	(2)
Change in state income taxes payable		8
Change in accrued interest	1	1
Change in operating working capital	$ 7	$ 12	[1]
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).

CHANGE IN OPERATING WORKING C54

CHANGE IN OPERATING WORKING CAPITAL - GTN's Carty Lateral Construction Accrual (Details) - USD ($) $ in Millions	6 Months Ended			12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	[1]	Dec. 31, 2015
Non-cash items
Capital expenditures	$ 16	$ 18
GTN
Non-cash items
Accruals for capital expenditures				$ 10
Capital expenditures	$ 10
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).

RELATED PARTY TRANSACTIONS (Det

RELATED PARTY TRANSACTIONS (Details) - USD ($) $ in Millions		Aug. 01, 2017	Jul. 31, 2017	Jul. 18, 2017	Jul. 07, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016		Dec. 31, 2016		Jun. 01, 2017
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable						$ 35		$ 35			$ 8	[1]
Amount included in receivables from related party						$ 1		1			2
Partnership distribution	[2]							160
Partnership's share of distributions								$ 68	$ 95	[1]
Great Lakes | Distribution declared | Subsequent Events
Capital and operating costs charged to the pipeline systems and amount payable
Partnership distribution				$ 15
Northern Border | Distribution declared | Subsequent Events
Capital and operating costs charged to the pipeline systems and amount payable
Partnership distribution					$ 14
Great Lakes
Capital and operating costs charged to the pipeline systems and amount payable
Interest acquired (as a percent)		46.45%				46.45%		46.45%
Great Lakes | Cash Distribution Paid | Subsequent Events
Capital and operating costs charged to the pipeline systems and amount payable
Partnership's share of distributions		$ 7
Great Lakes | FERC
Capital and operating costs charged to the pipeline systems and amount payable
Estimated revenue sharing provision						$ 7		$ 10			7.2
Northern Border
Capital and operating costs charged to the pipeline systems and amount payable
Interest acquired (as a percent)			50.00%			50.00%		50.00%
Northern Border | Cash Distribution Paid | Subsequent Events
Capital and operating costs charged to the pipeline systems and amount payable
Partnership's share of distributions			$ 7
Iroquois
Capital and operating costs charged to the pipeline systems and amount payable
Interest acquired (as a percent)						49.34%		49.34%					49.34%
Portland Natural Gas Transmission System
Capital and operating costs charged to the pipeline systems and amount payable
Interest acquired (as a percent)						11.81%	49.90%	11.81%	49.90%				11.81%
General Partner | Reimbursement of costs of services provided
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged						$ 1	$ 1	$ 2	$ 2
TransCanada's subsidiaries | Great Lakes
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable						$ 4		$ 4			4
Percentage of capital and operating costs charged						100.00%	100.00%	100.00%	100.00%
Amount included in receivables from related party						$ 1		$ 1			19
TransCanada's subsidiaries | Great Lakes | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged						$ 9	$ 7	$ 17	$ 14
Percentage of capital and operating costs charged						100.00%	100.00%	100.00%	100.00%
TransCanada's subsidiaries | Northern Border
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable						$ 4		$ 4			4
Percentage of capital and operating costs charged						100.00%	100.00%	100.00%	100.00%
TransCanada's subsidiaries | Northern Border | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged						$ 10	$ 9	$ 20	$ 15
Percentage of capital and operating costs charged						100.00%	100.00%	100.00%	100.00%
TransCanada's subsidiaries | Iroquois
Capital and operating costs charged to the pipeline systems and amount payable
Percentage of capital and operating costs charged						100.00%		100.00%
TransCanada's subsidiaries | Iroquois | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Percentage of capital and operating costs charged						100.00%		100.00%
TransCanada's subsidiaries | GTN
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable						$ 3		$ 3			3
TransCanada's subsidiaries | GTN | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged						9	$ 7	16	$ 13
Impact on the Partnership's net income attributable to controlling interests						7	6	14	11
TransCanada's subsidiaries | Bison
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable						1		1			1
TransCanada's subsidiaries | Bison | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged						1	1	2
Impact on the Partnership's net income attributable to controlling interests						1	1	2	2
TransCanada's subsidiaries | North Baja Pipeline, LLC
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable											1
TransCanada's subsidiaries | North Baja Pipeline, LLC | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged						1	1	2	2
Impact on the Partnership's net income attributable to controlling interests						1	1	2	2
TransCanada's subsidiaries | Tuscarora Gas Transmission Company
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable											1
TransCanada's subsidiaries | Tuscarora Gas Transmission Company | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged						1	1	2	2
Impact on the Partnership's net income attributable to controlling interests						1	1	2	2
TransCanada's subsidiaries | Portland Natural Gas Transmission System
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable						1		1			1
Amount included in receivables from related party						0		0			$ 0
TransCanada's subsidiaries | Portland Natural Gas Transmission System | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged						2	2	4	4
TransCanada's subsidiaries | Great Lakes | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Impact on the Partnership's net income attributable to controlling interests						$ 4	$ 3	$ 7	$ 6
TransCanada's subsidiaries | 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						43.00%	64.00%	57.00%	71.00%
TransCanada's subsidiaries | Northern Border | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Impact on the Partnership's net income attributable to controlling interests						$ 4	$ 3	$ 7	$ 6
TransCanada's subsidiaries | Portland Natural Gas Transmission System | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Impact on the Partnership's net income attributable to controlling interests						$ 1	$ 1	$ 2	$ 2
TransCanada's subsidiaries | Portland Natural Gas Transmission System | Transportation contracts | Total net revenues | Customer concentration risk
Capital and operating costs charged to the pipeline systems and amount payable
Percent of total revenues						2.00%	5.00%	1.00%	3.00%
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).
[2]	Recast to consolidate PNGTS for all periods presented. See Notes 2 and 6.

FAIR VALUE MEASUREMENTS - Estim

FAIR VALUE MEASUREMENTS - Estimated Fair Value of Debt (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Fair Value | Level 2
Financial Instruments
Fair value of debt	$ 2,465	$ 1,908

FAIR VALUE MEASUREMENTS - Inter

FAIR VALUE MEASUREMENTS - Interest Rate Swaps (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016		Jun. 30, 2017	Jun. 30, 2016		Dec. 31, 2016
Interest rate derivatives
Fair value of derivative asset, net							$ 0
Amortization of realized loss on derivative financial instruments	$ 1	$ 1	[1]	$ 1	$ 1	[1]
Amortization of derivatives loss	$ 1	1		1	1
Portland Natural Gas Transmission System
Interest rate derivatives
Payments for derivative instruments				$ 20.9
Interest acquired by Partnership (as a percent)	61.71%			61.71%
Net unamortized loss included in other comprehensive income	$ 1			$ 1			2
Amortization of derivatives loss				$ 1	1
Interest rate swaps | Term loan | TC PipeLines, LP 2013 Term Loan Facility due July 2018
Interest rate derivatives
Weighted average fixed interest rate (as a percent)	2.31%			2.31%
Hedges of cash flows | Interest rate swaps
Interest rate derivatives
Amortization of realized loss on derivative financial instruments	$ 0	(1)		$ 1	(3)
Hedges of cash flows | Interest rate swaps | Financial charges and other
Interest rate derivatives
Net realized loss related to the interest rate swaps	0	$ 1		0	$ 1
Hedges of cash flows | Interest rate swaps | Recurring fair value measurement | Level 2
Interest rate derivatives
Fair value of derivative asset, net	2			2
Designated as hedge | Interest rate swaps | Recurring fair value measurement | Level 2
Interest rate derivatives
Fair value of derivative asset, gross	$ 2			$ 2
Fair value of derivative liability, gross							0
Designated as hedge | Hedges of cash flows | Interest rate swaps | Level 2
Interest rate derivatives
Fair value of derivative asset, gross							1
Fair value of derivative liability, gross							$ 1
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).

ACCOUNTS RECEIVABLE AND OTHER58

ACCOUNTS RECEIVABLE AND OTHER (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
ACCOUNTS RECEIVABLE AND OTHER
Trade accounts receivable, net of allowance of nil	$ 35	$ 44
Imbalance receivable from affiliates	1	2
Other	1	1
Accounts receivable and other	37	47	[1]
Trade accounts receivable, allowance	$ 0	$ 0
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).

FINANCIAL CHARGES AND OTHER (De

FINANCIAL CHARGES AND OTHER (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016		Jun. 30, 2017	Jun. 30, 2016
FINANCIAL CHARGES AND OTHER
Interest Expense	$ 19	$ 16		$ 36	$ 35
PNGTS' amortization of derivative loss on derivative instruments	1	1		1	1
Net realized loss related to the interest rate swaps		1			1
Other Income	(1)	(1)		(1)	(2)
Financial charges and other	$ 19	$ 17	[1]	$ 36	$ 35	[1]
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).

CONTINGENCIES (Details)

CONTINGENCIES (Details) - Great Lakes v. Essar Steel Minnesota LLC, et al. - Great Lakes - USD ($) $ in Millions	Sep. 16, 2015	Oct. 29, 2009	Apr. 30, 2017
Contingencies
Judgement awarded			$ 31.5
Essar
Contingencies
Recovery sought		$ 33
Judgement awarded	$ 32.9

REGULATORY (Details)

REGULATORY (Details)	Jan. 06, 2017item
North Baja Pipeline, LLC | FERC
Goodwill and Regulatory Matters
Number of compression units	2

VARIABLE INTEREST ENTITIES - Co

VARIABLE INTEREST ENTITIES - Consolidated VIEs (Details) - USD ($) $ in Millions		Jun. 30, 2017	Dec. 31, 2016		Jun. 30, 2016		Dec. 31, 2015	[1]
ASSETS (LIABILITIES)
Cash and cash equivalents		$ 51	$ 64	[1]	$ 52	[1]	$ 55
Accounts receivable and other		37	47	[1]
Inventories		7	7	[1]
Other current assets		5	7	[1]
Equity investments		1,138	918	[1]	$ 918
Plant, property and equipment		2,148	2,180	[1]
Other assets	[1]		1
Accounts payable and accrued liabilities		(27)	(29)	[1]
Accounts payable to affiliates, net		(35)	(8)	[1]
Distributions payable	[1]		(3)
Accrued interest		(11)	(10)	[1]
Current portion of long-term debt		(57)	(52)	[1]
Long-term debt		(2,333)	(1,859)	[1]
Other liabilities		(28)	(28)	[1]
Consolidated VIEs | Restricted VIEs
ASSETS (LIABILITIES)
Cash and cash equivalents		13	14
Accounts receivable and other		26	33
Inventories		6	6
Other current assets		3	6
Equity investments		1,138	918
Plant, property and equipment		1,137	1,146
Other assets		1	2
Accounts payable and accrued liabilities		(20)	(21)
Accounts payable to affiliates, net		(39)	(32)
Distributions payable			(3)
Accrued interest		(1)	(2)
Current portion of long-term debt		(57)	(52)
Long-term debt		(304)	(337)
Other liabilities		(26)	(25)
Deferred state income tax		$ (10)	$ (10)
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).

INCOME TAXES (Details)

INCOME TAXES (Details) - USD ($) $ in Millions	6 Months Ended			12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016		Dec. 31, 2016
State income taxes
Total state income taxes	$ 1	$ 1	[1]
Portland Natural Gas Transmission System
Income Taxes
Effective income tax rate (as a percent)	3.80%			3.80%
State income taxes
Current	$ 1	8
Deferred		(7)
Total state income taxes	$ 1	$ 1
[1]	Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).

SUBSEQUENT EVENTS - Distributio

SUBSEQUENT EVENTS - Distributions (Details) - USD ($) $ / shares in Units, $ in Millions

Aug. 11, 2017

Aug. 01, 2017

Jul. 31, 2017

Jul. 27, 2017

Jul. 20, 2017

Jul. 18, 2017

Jul. 07, 2017

Jun. 01, 2017

Jun. 30, 2017

Jun. 30, 2016

Jun. 30, 2017

Jun. 30, 2016

Distributions

Partnership distribution

[1]

$ 160

Partnership's share of distributions

$ 68

$ 95

[2]

Northern Border

Distributions

Ownership interest (as a percent)

50.00%

50.00%

50.00%

Great Lakes

Distributions

Ownership interest (as a percent)

46.45%

46.45%

46.45%

Portland Natural Gas Transmission System

Distributions

Ownership interest (as a percent)

11.81%

11.81%

49.90%

11.81%

49.90%

Iroquois

Distributions

Ownership interest (as a percent)

49.34%

Portland Natural Gas Transmission System

Distributions

Ownership interest (as a percent)

11.81%

Total cash consideration

$ 53

Subsequent Events

Distributions

Total cash distribution

$ 74

Subsequent Events | Distribution declared | Northern Border

Distributions

Partnership distribution

$ 14

Subsequent Events | Distribution declared | Great Lakes

Distributions

Partnership distribution

$ 15

Subsequent Events | Distribution declared | Iroquois

Distributions

Partnership distribution

$ 28

Subsequent Events | Cash Distribution Paid | Northern Border

Distributions

Partnership's share of distributions

$ 7

Subsequent Events | Cash Distribution Paid | Great Lakes

Distributions

Partnership's share of distributions

$ 7

Subsequent Events | Cash Distribution Paid | Iroquois

Distributions

Partnership's share of distributions

$ 14

General Partner

Distributions

Partnership distribution

[1]

$ 6

TC PipeLines GP, Inc. | Subsequent Events

Distributions

General Partner cash distributions

$ 5

Ownership interest (as a percent)

2.00%

Total distribution for General Partner interest

$ 2

TC PipeLines GP, Inc. | General Partner

Distributions

Total distribution for General Partner interest

$ 1

$ 1

2

$ 2

TC PipeLines GP, Inc. | General Partner | Subsequent Events | Distribution declared

Distributions

Distribution declared for IDRs

$ 3

Common Units

Distributions

Total cash distribution

$ 68

$ 60

$ 135

$ 119

Number of units

69,000,000

65,900,000

[2]

69,000,000

65,900,000

[2]

Common Units | Subsequent Events

Distributions

Per Unit Distribution, declared (in dollars per unit)

$ 0.06

$ 1

Limited partners, Distribution declared

$ 69

Common Units | Limited Partners

Distributions

Partnership distribution

[1]

$ 129

Common Units | TC PipeLines GP, Inc. | Subsequent Events

Distributions

Limited Partners, Distributions paid

$ 6

Common Units | TC PipeLines GP, Inc. | Limited Partners

Distributions

Number of units

5,797,106

Common Units | TransCanada | Subsequent Events

Distributions

Limited Partners, Distributions paid

$ 11

Common Units | TransCanada | TC PipeLines GP, Inc.

Distributions

Number of units

11,287,725

[1]

Recast to consolidate PNGTS for all periods presented. See Notes 2 and 6.

[2]

Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).