TC Pipelines (TCP) 10-K 27 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Billions, except Share data, unless otherwise specified	Dec. 31, 2014	Feb. 24, 2015	Jun. 30, 2014
Document and Entity Information
Entity Registrant Name	TC PIPELINES LP
Entity Central Index Key	1075607
Document Type	10-K
Document Period End Date	31-Dec-14
Amendment Flag	FALSE
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$2.30
Entity Common Stock, Shares Outstanding		63,561,546
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Current Assets
Cash and cash equivalents	$26	$25	[1]
Accounts receivable and other (Note 19)	35	37
Inventories	7	7
Total current assets	68	69
Investments in unconsolidated affiliates (Note 4)	1,177	1,195
Plant, property and equipment (Note 5)	1,968	2,042
Goodwill	130	130
Other assets	6	7
Total assets	3,349	3,443
Current Liabilities
Accounts payable and accrued liabilities	23	19
Accounts payable to affiliates (Note 16)	15	29
Accrued interest	4	4
Short-term loan (Note 7)	170
Current portion of long-term debt (Note 7)	79	3
Total current liabilities	291	55
Long-term debt (Note 7)	1,446	1,575
Other liabilities (Note 8)	26	24
Total liabilities	1,763	1,654
Partners' Equity (Note 9)
Common units	1,325	1,322
General partner	29	28
Accumulated other comprehensive loss (Note 10)	-2	-1
Controlling interests	1,352	1,349
Non-controlling interests	234	440
Total partners' equity	1,586	1,789
Total liabilities and partners' equity	$3,349	$3,443
[1]	Recast as discussed in Note 2 and Note 6.

CONSOLIDATED_STATEMENTS_OF_INC

CONSOLIDATED STATEMENTS OF INCOME (USD $)	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
CONSOLIDATED STATEMENTS OF INCOME
Transmission revenues	$336	$341	[1]	$343	[1]
Equity earnings from unconsolidated affiliates (Note 4)	88	67	[1]	99	[1]
Operation and maintenance expenses	-54	-55	[1]	-57	[1]
Property taxes	-21	-23	[1]	-25	[1]
General and administrative	-9	-9	[1]	-6	[1]
Depreciation	-86	-86	[1]	-85	[1]
Financial charges and other (Note 11)	-50	-44	[1]	-40	[1]
Net income	204	191	[1]	229	[1]
Net income attributable to non-controlling interests	32	36	[1]	37	[1]
Net income attributable to controlling interests	172	155	[1]	192	[1]
Net income attributable to controlling interests allocation (Note 12)
Common units	168	126	[1]	134	[1]
General Partner	4	3	[1]	3	[1]
Net income allocated to controlling interests	$172	$129	[1]	$137	[1]
Net income per common unit (Note 12) - basic (in dollars per unit)	$2.67	$2.13		$2.51
Net income per common unit (Note 12) - diluted (in dollars per unit)	$2.67	$2.13		$2.51
Weighted average common units outstanding (millions) - basic (in units)	62.7	58.9		53.5
Weighted average common units outstanding (millions) - diluted (in units)	62.7	58.9		53.5
Common units outstanding, end of year (millions) (in units)	63.6	62.3		53.5
[1]	Recast as discussed in Note 2 and Note 6.

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Net income	$204	$191	[1]	$229	[1]
Other comprehensive income
Change in fair value of cash flow hedges (Note 18)	-1
Reclassification to net income of gains and losses on cash flow hedges (Note 10)			[1]		[1]
Other comprehensive income	-1
Total comprehensive income	203	191	[1]	229	[1]
Comprehensive income attributable to non-controlling interests	32	36	[1]	37	[1]
Comprehensive income attributable to controlling interests	$171	$155	[1]	$192	[1]
[1]	Recast as discussed in Note 2 and Note 6.

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Cash Generated From Operations
Net income	$204		$191	[1]	$229	[1]
Depreciation	86		86	[1]	85	[1]
Amortization of debt issue costs (Note 11)	1		1	[1]	1	[1]
Change in other long-term liabilities			2	[1]
Change in operating working capital (Note 14)	17		-8	[1]
Total cash generated from operations	308		272	[1]	315	[1]
Investing Activities
Adjustment to the 2011 Acquisition			1	[1]
Capital expenditures	-10		-15	[1]	-36	[1]
Change in affiliate demand loan receivable			21	[1]	20	[1]
Total investing activities	-234		-920	[1]	16	[1]
Financing Activities
Distributions paid (Note 13)	-212		-188	[1]	-169	[1]
Distributions paid to non-controlling interests	-50		-52	[1]	-53	[1]
Change in affiliate demand loan payable			-15	[1]
Long-term debt issued (Note 7)	35		937	[1]	8	[1]
Short-term loan issued (Note 7)	170
Long-term debt repaid (Note 7)	-89		-372	[1]	-62	[1]
Debt issue costs			-2	[1]
Equity contribution from Bison's former parent (Note 16)			18	[1]
Distributions paid to former parent of GTN and Bison			-37	[1]	-81	[1]
Total financing activities	-73		670	[1]	-357	[1]
Increase/(decrease) in cash and cash equivalents	1		22	[1]	-26	[1]
Cash and cash equivalents, beginning of year	25	[1]	3	[1]	29	[1]
Cash and cash equivalents, end of year	26		25	[1]	3	[1]
Interest payments made	47		42	[1]	42	[1]
Supplemental information about non-cash investing and financing activities
Accrual for Carty Lateral consideration payment (Note 16)			25	[1]
ATM Equity Issuance Program
Financing Activities
Equity issuance, net (Note 9)	73
Equity Issuance, May 2013
Financing Activities
Equity issuance, net (Note 9)			381	[1]
GTN and Bison
Investing Activities
Acquisition of additional interests, net of cash acquired (Note 6)			-921	[1]
GTN
Investing Activities
Acquisition of interest	-25
Bison
Investing Activities
Acquisition of remaining 30 percent interest	-217
Great Lakes
Investing Activities
Cumulative distributions in excess of equity earnings	9		14	[1]	17	[1]
Investment in unconsolidated affiliate (Note 4)	-9		-9	[1]	-9	[1]
Northern Border
Investing Activities
Cumulative distributions in excess of equity earnings	18		20	[1]	24	[1]
Investment in unconsolidated affiliate (Note 4)			($31)	[1]
[1]	Recast as discussed in Note 2 and Note 6.

CONSOLIDATED_STATEMENT_OF_CHAN

CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY (USD $)		Common Units (Limited Partners)	Common Units (Limited Partners)	Common Units (Limited Partners)	Common Units (Limited Partners)	Common Units (Limited Partners)	Common Units (Limited Partners)	General Partner	General Partner	General Partner	General Partner	General Partner	Accumulated Other Comprehensive Loss		Non-controlling interests	Non-controlling interests	Non-controlling interests	Equity of former parent	Equity of former parent	Equity of former parent	GTN and Bison	Bison	GTN and Bison	Bison	Equity Issuance, May 2013	ATM Equity Issuance Program	Total
In Millions, unless otherwise specified		Former parent, TransCanada subsidiaries	GTN and Bison	Bison	Equity Issuance, May 2013	ATM Equity Issuance Program		Former parent, TransCanada subsidiaries	GTN and Bison	Equity Issuance, May 2013	ATM Equity Issuance Program				Bison	Bison		Former parent, TransCanada subsidiaries	GTN and Bison	Bison
		GTN and Bison						GTN and Bison										GTN and Bison
Partners' Equity at beginning of year at Dec. 31, 2011	[1]						$1,307					$27	($1)	[2]			$465		$698								$2,496
Partners' Equity at beginning of year (in units) at Dec. 31, 2011							53.5
Increase (Decrease) in Partners' Equity
Net income	[1]						188					4					37										229
Net income attributed to GTN and Bison's former parent	[1]	-54						-1										55
Distribution paid related to equity of former parent																			-81		-81
Effect of conversion to an LLC by GTN and other (Note 6)	[1]																-1		1
Distributions paid	[1]						-166					-3					-53										-222
Partners' Equity at end of year at Dec. 31, 2012	[1]						1,275					27	-1	[2]			448		673								2,422
Partners' Equity at End of Year (in units) at Dec. 31, 2012							53.5
Increase (Decrease) in Partners' Equity
Net income	[1]						152					3					36										191
Net income attributed to GTN and Bison's former parent	[1]	-26																26
Distribution paid related to equity of former parent																			-37		-37
Equity issuance, net (Note 9)					373					8															381
Equity issuance (Note 9) (in units)					8.8
Acquisition of the remaining 30 percent interest, 2014; Excess purchase price paid over net acquired assets, 2013 (Note 6)			-268						-6														-274
Distributions paid							-184					-4					-52										-240
Former parent carrying amount of acquired entities																			-672		-672
Adjustment to the 2011 Acquisition							1																				1
Other							-1																				-1
Equity contributions from former parent															8					10		18
Partners' Equity at end of year at Dec. 31, 2013							1,322					28	-1	[2]			440										1,789
Partners' Equity at End of Year (in units) at Dec. 31, 2013							62.3
Increase (Decrease) in Partners' Equity
Net income							168					4					32										204
Other comprehensive loss													-1	[2]													-1
Equity issuance, net (Note 9)						71					2															73
Equity issuance (Note 9) (in units)						1.3
Acquisition of the remaining 30 percent interest, 2014; Excess purchase price paid over net acquired assets, 2013 (Note 6)				-29												-188								-217
Distributions paid							-207					-5					-50										-262
Partners' Equity at end of year at Dec. 31, 2014							$1,325					$29	($2)	[2]			$234										$1,586
Partners' Equity at End of Year (in units) at Dec. 31, 2014							63.6
[1]	Recast as discussed in Note 2 and Note 6.
[2]	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 less than $1 million. These estimates assume constant interest rates over time; however, the amounts reclassified will vary based on actual value of interest rates at the date of settlement.

CONSOLIDATED_STATEMENT_OF_CHAN1

CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY (Parenthetical) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014
Maximum
Losses related to cash flow hedges reported in Accumulated Other Comprehensive Loss
Losses expected to be reclassified to net income in the next 12 months	$1

ORGANIZATION

ORGANIZATION	12 Months Ended
	Dec. 31, 2014
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 the following interests in natural gas pipeline systems:
	Pipeline	Length	Description	Ownership
	Gas Transmission Northwest LLC (GTN)	1,353 miles	Extends between an interconnection near Kingsgate, British Columbia, Canada at the Canadian border to a point near Malin, Oregon at the California border and delivers natural gas to the Pacific Northwest and to California. TransCanada owns the remaining 30 percent of GTN (See Note 22 – Subsequent Events).	70 percent
	Northern Border Pipeline Company (Northern Border)	1,408 miles	Extends between the Canadian border near Port of Morgan, Montana to a terminus near North Hayden, Indiana, south of Chicago. Northern Border is capable of receiving natural gas from Canada, the Williston Basin and Rocky Mountain Basin. ONEOK Partners, L.P. owns the remaining 50 percent of Northern Border.	50 percent
	Bison Pipeline LLC (Bison)	303 miles	Extends from a location near Gillette, Wyoming to Northern Border's pipeline system in North Dakota. Bison transports natural gas from the Powder River Basin to Midwest markets.	100 percent
	Great Lakes Gas Transmission Limited Partnership (Great Lakes)	2,115 miles	Connects with the TransCanada Mainline at the Canadian border near Emerson, Manitoba, Canada and St. Clair, Michigan, near Detroit. Great Lakes is a bi-directional pipeline that can receive and deliver natural gas at multiple points along its system. TransCanada owns the remaining 53.55 percent of Great Lakes.	46.45 percent
	North Baja Pipeline, LLC (North Baja)	86 miles	Extends between an interconnection with the El Paso Natural Gas Company pipeline near Ehrenberg, Arizona and an interconnection with a natural gas pipeline near Ogilby, California on the Mexican border. North Baja is a bi-directional pipeline.	100 percent
	Tuscarora Gas Transmission Company (Tuscarora)	305 miles	Extends between the GTN pipeline near Malin, Oregon to its terminus near Reno, Nevada and delivers natural gas in northeastern California and northwestern Nevada.	100 percent
	The Partnership is managed by its General Partner, TC PipeLines GP, Inc. (General Partner), an indirect wholly-owned subsidiary of TransCanada. The General Partner provides management and operating services for the Partnership and is reimbursed for its costs and expenses. The General Partner owns 5,797,106 common units, which together with its effective two percent general partner interest represents an effective 10.9 percent interest in the Partnership at December 31, 2014. TransCanada also indirectly holds additional 11,287,725 common units representing a 17.4 percent limited partner interest in the Partnership for a total interest in the Partnership of 28.3 percent at December 31, 2014.

SIGNIFICANT_ACCOUNTING_POLICIE

SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2014
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 financial statements and notes present the financial position of the Partnership as of December 31, 2014 and 2013 and the results of its operations, cash flows and changes in partners' equity for the years ended December 31, 2014, 2013 and 2012.
	(a)    Basis of Presentation
	The Partnership consolidates its investments in GTN, Bison, North Baja and Tuscarora, over which it is able to exercise control. To the extent there are interests owned by other parties, these interests are included in non-controlling interests. The Partnership uses the equity method of accounting for its investments in Northern Border and Great Lakes, over which it is able to exercise significant influence.
	On October 1, 2014, the Partnership acquired the remaining 30 percent interest in Bison from a subsidiary of TransCanada (the 2014 Acquisition), which resulted in Bison being wholly-owned by the Partnership. Prior to this transaction, the remaining 30 percent interest held by a subsidiary of TransCanada was reflected as non-controlling interest in the consolidated financial statements. The 2014 Acquisition of this already-consolidated entity was accounted for as a transaction between entities under common control, similar to a pooling of interests, whereby the acquired interest was recorded at TransCanada's carrying value and the total excess purchase price paid was recorded as a reduction in Partners' Equity. Refer to Note 6 for additional disclosure regarding the 2014 Acquisition.
	On July 1, 2013, the Partnership acquired a 45 percent membership interest in each of GTN and Bison (the 2013 Acquisition) from subsidiaries of TransCanada increasing the Partnership's ownership in each of GTN and Bison to 70 percent. The 2013 Acquisition was accounted for as a transaction between entities under common control, similar to a pooling of interests, whereby the assets and liabilities of GTN and Bison were recorded at TransCanada's carrying value and the Partnership's historical financial information, except net income per common unit, was recast to consolidate GTN and Bison for all periods presented. Refer to Note 6 for additional disclosure regarding the 2013 Acquisition.
	(b)    Use of Estimates
	The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Although management believes these estimates are reasonable, actual results could differ from these estimates.
	(c)    Cash and Cash Equivalents
	The Partnership's cash and cash equivalents consist of cash and highly liquid short-term investments with original maturities of three months or less and are recorded at cost, which approximates fair value.
	(d)    Trade Accounts Receivable
	Trade accounts receivable are recorded at the invoiced amount and do not bear interest. We review our accounts receivable regularly and record allowances for doubtful accounts using the specific identification method.
	(e)    Inventories
	Inventories primarily consist of materials and supplies and are carried at the lower of weighted average cost or market.
	(f)    Plant, Property and Equipment
	Plant, property and equipment are stated at original cost. Costs of restoring the land above and around the pipeline are capitalized to pipeline facilities and depreciated over the remaining life of the related pipeline facilities. Pipeline facilities and compression equipment have an estimated useful life of 20 to 77 years and metering and other equipment ranges from 5 to 77 years. Depreciation is calculated on a straight-line composite basis over the assets' estimated useful lives. Repair and maintenance costs are expensed as incurred. Costs that are considered a betterment are capitalized.
	An allowance for funds used during construction, using the rate of return on rate base approved by the Federal Energy Regulatory Commission (FERC), is capitalized and included in the cost of plant, property and equipment. Amounts included in construction work in progress are not amortized until transferred into service.
	(g)    Impairment of Equity Investments
	We review our equity method investments when a significant event or change in circumstances has occurred that may have an adverse effect on the fair value of each investment. When such events or changes occur, we compare the estimated fair value to the carrying value of the related investment. We also perform this evaluation every reporting period for each investment for which the carrying value has exceeded the fair value in the prior period. We calculate the estimated fair value of an investment in an equity method investee using an income approach and market approach. The development of fair value estimates requires significant judgment including estimates of future cash flows, which is dependent on internal forecasts, estimates of the long-term rate of growth for the investee, estimates of the useful life over which cash flows will occur, and determination of weighted average cost of capital. The estimates used to calculate the fair value of an investee can change from year to year based on operating results and market conditions. Changes in these estimates and assumptions could materially affect the determination of fair value and our assessment as to whether an investment in an equity method investee has suffered an impairment.
	If the estimated fair value of an investment is less than its carrying value, we are required to determine if the decline in fair value is other than temporary. This determination considers the aforementioned valuation methodologies, the length of time and the extent to which fair value has been less than carrying value, the financial condition and near-term prospects of the investee, including any specific events which may influence the operations of the investee, the intent and ability of the holder to retain its investment in the investee for a period of time sufficient to allow for any anticipated recovery in market value, and other facts and circumstances. If the fair value of an investment is less than its carrying value and the decline in value is determined to be other than temporary, we record an impairment charge.
	(h)    Impairment of Long-lived Assets
	The Partnership reviews long-lived assets, such as plant, property and equipment for impairment whenever events or changes in circumstances indicate the carrying value may not be recoverable. If the total of the estimated undiscounted future cash flows is less than the carrying value of the assets, an impairment loss is recognized for the excess of the carrying value over the fair value of the assets.
	(i)    Partners' Equity
	Costs incurred in connection with the issuance of units are deducted from the proceeds received.
	(j)    Revenue Recognition
	Transmission revenues are recognized in the period in which the service is provided. When a rate case is pending final FERC approval, a portion of the revenue collected is subject to possible refund. As of December 31, 2014, 2013 and 2012, the Partnership has not recognized any transmission revenue that is subject to possible refund.
	(k)    Income Taxes
	The Partnership is not subject to federal or state income tax. The tax effect of the Partnership's activities accrues to its partners. The Partnership's taxable income or loss, which may vary substantially from the net income or loss reported in the consolidated statement of income, is includable in the federal income tax returns of each partner. The aggregate difference in the basis of the Partnership's net assets for financial and income tax purposes cannot be readily determined because all information regarding each partner's tax attributes related to the partnership is not available.
	As a result of the recast of the Partnership's historical financial information (refer to Note 2 (a)), the Partnership included income taxes in its consolidated financial statements for the year ended December 31, 2011. Those income taxes relate to GTN for the periods prior to April 1, 2011. GTN is no longer subject to income taxes and settled all current and deferred income tax balances pursuant to GTN's tax-sharing agreement with TransCanada PipeLine USA Ltd. upon conversion to an LLC on April 1, 2011. GTN used the Asset and Liability method of accounting for income taxes for the periods prior to April 1, 2011.
	(l)    Acquisitions and Goodwill
	The Partnership accounts for business acquisitions from third parties using the acquisition method of accounting and, accordingly, the assets and liabilities of the acquired entities are recorded at their estimated fair values at the date of acquisition. The excess of the purchase price over the fair value of net assets acquired is attributed to goodwill. Goodwill is not amortized and is tested on an annual basis for impairment or more frequently if any indicators of impairment are evident. The Partnership initially assesses qualitative factors to determine whether events or changes in circumstances indicate that the goodwill might be impaired. If the Partnership does not conclude that it is more likely than not that fair value of the reporting unit is greater than its carrying value, the first step of the two-step impairment test is performed by comparing the fair value of the reporting unit to its book value, which includes goodwill. If the fair value is less than book value, an impairment is indicated and a second step is performed to measure the amount of the impairment. In the second step, the implied fair value of goodwill is calculated by deducting the recognized amounts of all tangible and intangible net assets of the reporting unit from the fair value determined in the initial assessment. If the carrying value of goodwill exceeds the calculated implied fair value of goodwill, an impairment charge is recorded.
	The Partnership accounts for business acquisitions between itself and TransCanada as transactions between entities under common control. Using this approach, the assets and liabilities of the acquired entities are recorded at TransCanada's carrying value. In the event recasting is required, the Partnership's historical financial information will be recast, except net income per common unit, to include the acquired entities for all periods presented. If the fair market value paid for the acquired entities is greater than the recorded net assets of the acquired entities, the excess purchase price paid is recorded as a reduction in Partners' Equity. Similarly, if the fair market value paid for the acquired entities is less than the recorded net assets of the acquired entities, the excess of assets acquired is recorded as an increase in Partners' Equity.
	(m)    Fair Value Measurements
	For cash and cash equivalents, receivables, accounts payable and certain accrued expenses, the carrying amount approximates fair value due to the short maturities of these instruments. For long-term debt instruments and the interest rate swap agreements, fair value is estimated based upon market values (if applicable) or on the current interest rates available to us for debt with similar terms and remaining maturities. Considerable judgment is required in developing these estimates.
	(n)    Derivative Financial Instruments and Hedging Activities
	The Partnership recognizes all derivative instruments as either assets or liabilities in the balance sheet at their respective fair values. For derivatives designated in hedging relationships, changes in the fair value are either offset through earnings against the change in fair value of the hedged item attributable to the risk being hedged or recognized in accumulated other comprehensive income, to the extent the derivative is effective at offsetting the changes in cash flows being hedged until the hedged item affects earnings.
	The Partnership only enters into derivative contracts that it intends to designate as a hedge of a forecasted transaction or the variability of cash flows to be received or paid related to a recognized asset or liability (cash flow hedge). For all hedging relationships, the Partnership formally documents the hedging relationship and its risk management objective and strategy for undertaking the hedge, the hedging instrument, the hedged transaction, the nature of the risk being hedged, how the hedging instrument's effectiveness in offsetting the hedged risk will be assessed prospectively and retrospectively, and a description of the method used to measure ineffectiveness. The Partnership also formally assesses, both at the inception of the hedging relationship and on an ongoing basis, whether the derivatives that are used in hedging relationships are highly effective in offsetting changes in cash flows of hedged transactions. For derivative instruments that are designated and qualify as part of a cash flow hedging relationship, the effective portion of the gain or loss on the derivative is reported as a component of other comprehensive income and reclassified into earnings in the same period or periods during which the hedged transaction affects earnings. Gains and losses on the derivative representing either hedge ineffectiveness or hedge components excluded from the assessment of effectiveness are recognized in current earnings.
	The Partnership discontinues hedge accounting prospectively when it determines that the derivative is no longer effective in offsetting cash flows attributable to the hedged risk, the derivative expires or is sold, terminated, or exercised, the cash flow hedge is de-designated because a forecasted transaction is not probable of occurring, or management determines to remove the designation of the cash flow hedge.
	In all situations in which hedge accounting is discontinued and the derivative remains outstanding, the Partnership continues to carry the derivative at its fair value on the balance sheet and recognizes any subsequent changes in its fair value in earnings. When it is probable that a forecasted transaction will not occur, the Partnership discontinues hedge accounting and recognizes immediately in earnings gains and losses that were accumulated in other comprehensive income related to the hedging relationship.
	(o)    Asset Retirement Obligation
	The Partnership recognizes the fair value of a liability for asset retirement obligations in the period in which it is incurred, when a legal obligation exists and a reasonable estimate of fair value can be made. The fair value is added to the carrying amount of the associated asset and the liability is accreted through charges to operating expenses.
	The scope and timing of asset retirements related to natural gas pipelines is indeterminable. As a result, the Partnership has recorded no asset retirement obligations as of December 31, 2014 and 2013.
	(p)    Government Regulation
	The Partnership's subsidiaries are subject to regulation by FERC. Under regulatory accounting principles, certain assets or liabilities that result from the regulated ratemaking process may be recorded that would not be recorded under GAAP for non-regulated entities. The timing of recognition of certain revenues and expenses in our regulated business may differ from that otherwise expected under GAAP to appropriately reflect the economic impact of the regulators' decisions regarding revenues and rates. The Partnership regularly evaluates the continued applicability of regulatory accounting, considering such factors as regulatory changes, the impact of competition, and the ability to recover regulatory assets. The Partnership had no material regulatory assets as of December 31, 2014 and 2013. Regulatory liabilities are included in other long-term liabilities (refer to Note 8). Allowance for funds used during construction is capitalized and included in plant, property and equipment.
	(q)    Debt Issuance Costs
	Costs related to the issuance of debt are deferred and amortized using the effective interest rate method over the term of the related debt.

ACCOUNTING_PRONOUNCEMENTS

ACCOUNTING PRONOUNCEMENTS	12 Months Ended
	Dec. 31, 2014
ACCOUNTING PRONOUNCEMENTS
ACCOUNTING PRONOUNCEMENTS	NOTE 3 ACCOUNTING PRONOUNCEMENTS
	Revenue from contracts with customers
	In May 2014, the FASB issued new guidance on Revenue from Contracts with Customers (Topic 606). This guidance supersedes the revenue recognition requirements in Topic 605, Revenue Recognition and most industry-specific guidance. This new guidance requires that an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. This new guidance is effective from January 1, 2017 with two methods in which the amendment can be applied; (1) retrospectively to each prior reporting period presented, or (2) retrospectively with the cumulative effect recognized at the date of initial application. Early application is not permitted. The Partnership is currently evaluating the impact of the adoption of this Accounting Standards Update (ASU) and has not yet determined the effect on its consolidated financial statements.

INVESTMENTS_IN_UNCONSOLIDATED_

INVESTMENTS IN UNCONSOLIDATED AFFILIATES	12 Months Ended
	Dec. 31, 2014
INVESTMENTS IN UNCONSOLIDATED AFFILIATES
INVESTMENTS IN UNCONSOLIDATED AFFILIATES	NOTE 4 INVESTMENTS IN UNCONSOLIDATED AFFILIATES
	Great Lakes and Northern Border are regulated by FERC and are operated by TransCanada. We use the equity method of accounting for our interests in our equity investees.
	Equity Earnings from Unconsolidated Affiliates					Investment in Unconsolidated Affiliates
	Year ended December 31					December 31
	Ownership
	Interest at
	(millions of dollars)	December 31, 2014		2014		2013		2012	2014	2013
	Northern Border(a)		50%		69		64		72	505	523
	Great Lakes		46.45%		19		3		27	672	672
					88		67		99	1,177	1,195
	(a)	Equity earnings from Northern Border is net of the 12-year amortization of a $10 million transaction fee paid to the operator of Northern Border at the time of the Partnership's additional 20 percent acquisition in April 2006.
	Northern Border
	The Partnership owns a 50 percent general partner interest in Northern Border. The other 50 percent partnership interest in Northern Border is held by ONEOK Partners, L.P., a publicly traded limited partnership.
	TC PipeLines Intermediate Limited Partnership, as one of the general partners, may be exposed to the commitments and contingencies of Northern Border. The Partnership holds a 98.9899 percent limited partnership interest in TC PipeLines Intermediate Limited Partnership.
	Northern Border has a FERC-approved settlement agreement which established maximum long-term transportation rates and charges on the Northern Border system effective January 1, 2013. The Northern Border Settlement also includes a three-year moratorium on filing rate cases and requires Northern Border to file for new rates no later than January 1, 2018.
	The Partnership recorded no undistributed earnings from Northern Border for the years ended December 31, 2014, 2013 and 2012.
	At December 31, 2014, the Partnership had a $117 million (2013 – $118 million) difference between the carrying value of Northern Border and the underlying equity in the net assets primarily resulting from the recognition and inclusion of goodwill in the Partnership's investment in Northern Border relating to the Partnership's April 2006 acquisition of an additional 20 percent general partnership interest in Northern Border.
	The summarized financial information for Northern Border is as follows:
	December 31 (millions of dollars)			2014		2013
	Assets
	Cash and cash equivalents			41		27
	Other current assets			34		34
	Plant, property and equipment, net			1,163		1,197
	Other assets			34		33
				1,272		1,291
	Liabilities and Partners' Equity
	Current liabilities			64		51
	Deferred credits and other			22		19
	Long-term debt			411		411
	Partners' equity
		Partners' capital		777		812
		Accumulated other comprehensive loss		(2	)	(2	)
				1,272		1,291
	Year ended December 31 (millions of dollars)		2014		2013		2012
	Transmission revenues		293		286		311
	Operating expenses		(72	)	(75	)	(79	)
	Depreciation		(59	)	(58	)	(63	)
	Financial charges and other		(22	)	(23	)	(24	)
	Net income		140		130		145
	Great Lakes
	The Partnership owns a 46.45 percent general partner interest in Great Lakes. TransCanada owns the other 53.55 percent partnership interest. TC GL Intermediate Limited Partnership, as one of the general partners, may be exposed to the commitments and contingencies of Great Lakes. The Partnership holds a 98.9899 percent limited partnership interest in TC GL Intermediate Limited Partnership.
	On November 14, 2013, FERC approved a settlement between Great Lakes and its customers to modify its transportation rates effective November 1, 2013. The settlement increases maximum recourse transportation rates by approximately 21 percent. The settlement includes a moratorium on filing rate cases or challenging the settlement rates until March 31, 2015 and requires that Great Lakes file to have new rates in effect no later than January 1, 2018.
	The Partnership recorded no undistributed earnings from Great Lakes for the years ended December 31, 2014, 2013, and 2012.
	At December 31, 2014, the Partnership had a $458 million (2013 – $458 million) difference between the carrying value of Great Lakes and the underlying equity in the net assets primarily resulting from the recognition and inclusion of goodwill in the Partnership's investment in Great Lakes relating to the Partnership's February 2007 acquisition of a 46.45 percent general partner interest in Great Lakes.
	The Partnership made equity contributions to Great Lakes of $4 million and $5 million in the first and fourth quarter of 2014, respectively. These amounts represent the Partnership's 46.45 percent share of a $9 million and $10 million cash call from Great Lakes to make scheduled debt repayments.
	The summarized financial information for Great Lakes is as follows:
	December 31 (millions of dollars)		2014		2013
	Assets
	Current assets		66		52
	Plant, property and equipment, net		748		771
			814		823
	Liabilities and Partners' Equity
	Current liabilities		38		28
	Long-term debt, including current maturities		316		335
	Partners' equity		460		460
			814		823
	Year ended December 31 (millions of dollars)		2014		2013		2012
	Transmission revenues		146		124		182
	Operating expenses		(53	)	(60	)	(66	)
	Depreciation		(28	)	(31	)	(31	)
	Financial charges and other		(25	)	(27	)	(28	)
	Net income		40		6		57

PLANT_PROPERTY_AND_EQUIPMENT

PLANT, PROPERTY AND EQUIPMENT	12 Months Ended
	Dec. 31, 2014
PLANT, PROPERTY AND EQUIPMENT
PLANT, PROPERTY AND EQUIPMENT	NOTE 5 PLANT, PROPERTY AND EQUIPMENT
	The following table includes plant, property and equipment from our consolidated subsidiaries.
	2014				2013
	December 31 (millions of dollars)
		Cost	Accumulated		Net Book	Cost	Accumulated		Net Book
			Depreciation		Value		Depreciation		Value
	Pipeline	2,038	(574	)	1,464	2,045	(522	)	1,523
	Compression	514	(126	)	388	520	(120	)	400
	Metering and other	145	(37	)	108	146	(32	)	114
	Construction in progress	8	–		8	5	–		5
		2,705	(737	)	1,968	2,716	(674	)	2,042

ACQUISITIONS

ACQUISITIONS	12 Months Ended
	Dec. 31, 2014
ACQUISITIONS
ACQUISITIONS	NOTE 6 ACQUISITIONS
	2014 Acquisition
	On October 1, 2014, the Partnership acquired the remaining 30 percent interest in Bison from a subsidiary of TransCanada. The total purchase price of the 2014 Acquisition was $215 million plus purchase price adjustments of $2 million. The acquisition of Bison was financed through combinations of (i) net proceeds from the ATM Program (refer to Note 9), and (ii) short-term financing (refer to Note 7).
	Prior to this transaction, the remaining 30 percent interest held by a subsidiary of TransCanada was reflected as non-controlling interest in the Partnership's consolidated financial statements. The 2014 Acquisition of this already-consolidated entity was accounted as a transaction between entities under common control, similar to a pooling of interests, whereby the acquired interest was recorded at TransCanada's carrying value and the total excess purchase price paid was recorded as a reduction in Partners' Equity.
	The purchase price was allocated as follows:
	(millions of dollars)
	Total cash consideration	217
	TransCanada's carrying value of non-controlling interest at October 1, 2014	188
	Excess purchase price	29
	The excess purchase price of $29 million was recorded as a reduction in Partners' Equity.
	2013 Acquisition
	On July 1, 2013, the Partnership acquired a 45 percent membership interest in each of GTN and Bison from subsidiaries of TransCanada, increasing the Partnership's ownership in each GTN and Bison to 70 percent. The total purchase price of the 2013 Acquisition was $1,050 million plus purchase price adjustments. The purchase price consisted of (i) $750 million for the GTN membership interest (less $146 million, which reflected 45 percent of GTN's outstanding debt at the time of the 2013 Acquisition), (ii) $300 million for the membership interest in Bison, (iii) $17 million in working capital adjustments and (iv) Carty Lateral consideration of $25 million (see below).
	The resulting $921 million (after working capital adjustments) paid by the Partnership was financed through a combination of (i) a public offering of 8,855,000 common units at $43.85 per common unit resulting in net proceeds of $373 million (refer to note 9), (ii) borrowing of $500 million in term loans (refer to note 7), (iii) a capital contribution from the General Partner of $8 million which was required to maintain the General Partner's effective two percent general partner interest in the Partnership (refer to note 9), and (iv) a draw on the Partnership's existing $500 million Senior Credit Facility and cash on hand.
	Pursuant to the acquisition agreement between the Partnership and TransCanada relating to the Partnership's acquisition of an additional 45 percent membership interest in GTN, the Partnership agreed to make an additional payment of $25 million to TransCanada if Portland General Electric Company executes a firm transportation service agreement by December 31, 2014 containing agreed terms and relating to transportation on GTN's proposed Carty Lateral. On December 11, 2013, Portland General Electric Company executed this firm transportation service agreement relating to transportation on GTN's proposed Carty Lateral. As a result, the Partnership paid an additional $25 million on April 11, 2014. This amount was included in accounts payable to affiliates as of December 31, 2013.
	The 2013 Acquisition was accounted for as a transaction between entities under common control, similar to a pooling of interests, whereby the assets and liabilities of GTN and Bison were recorded at TransCanada's carrying value and the Partnership's historical financial information, except net income per common unit, was recast to consolidate GTN and Bison for all periods presented.
	The purchase price was recorded as follows:
	(millions of dollars)
	Current assets	67
	Property, plant and equipment, net	1,792
	Other assets	1
	Current liabilities	(20	)
	Other liabilities	(21	)
	Long-term debt	(325	)
		1,494
	Non-controlling interest	(448	)
	Carrying value of pre-existing 25% interest in each of GTN and Bison	(374	)
	Carrying value of acquired 45% interest in each of GTN and Bison	672
	Excess purchase price over net assets acquired (includes Carty Lateral consideration)	274
	Total cash consideration including $25 million Carty Lateral consideration	946
	As the fair market value for the additional 45 percent interests in each of GTN and Bison was greater than the acquired net assets of GTN and Bison by $262 million and $12 million, respectively, the total excess purchase price of $274 million was recorded in Partners' Equity, including the Carty Lateral consideration. The retrospective consolidation of GTN and Bison increased net income attributable to controlling interests by $26 million for the year ended December 31, 2013 and by $55 million for the year ended December 31, 2012. These amounts are however excluded from equity attributable to controlling interests and did not impact historical net income per common unit as the pre-acquisition earnings was allocated to TransCanada (refer to Note 12).

CREDIT_FACILITIES_SHORTTERM_LO

CREDIT FACILITIES, SHORT-TERM LOAN FACILITY AND LONG-TERM DEBT	12 Months Ended
	Dec. 31, 2014
CREDIT FACILITIES, SHORT-TERM LOAN FACILITY AND LONG-TERM DEBT
CREDIT FACILITIES, SHORT-TERM LOAN FACILITY AND LONG-TERM DEBT	NOTE 7    CREDIT FACILITIES, SHORT-TERM LOAN FACILITY AND LONG-TERM DEBT
		2014	2013
	December 31 (millions of dollars)
	Senior Credit Facility due 2017	330	380
	Term Loan Facility due 2018	500	500
	Short-Term Loan Facility due 2015	170	–
	4.65% Unsecured Senior Notes due 2021	350	349
	5.09% Unsecured Senior Notes due 2015	75	75
	5.29% Unsecured Senior Notes due 2020	100	100
	5.69% Unsecured Senior Notes due 2035	150	150
	3.82% Series D Senior Notes due 2017	20	24
		1,695	1,578
	Less: current portion	249	3
		1,446	1,575
	The Partnership's Senior Credit Facility consists of a $500 million senior revolving credit facility with a banking syndicate, maturing November 20, 2017, under which $330 million was outstanding at December 31, 2014 (2013 – $380 million), leaving $170 million available for future borrowing.
	At the Partnership's option, the interest rate on the outstanding borrowings under the Senior Credit Facility may be lenders' base rate or the London Interbank Offered Rate (LIBOR) plus, in either case, an applicable margin that is based on the Partnership's long-term unsecured credit ratings. The Senior Credit Facility permits the Partnership to specify the portion of the borrowings to be covered by specific interest rate options and, for LIBOR-based borrowings, to specify the interest rate period. The Partnership is required to pay a commitment fee based on its credit rating and on the unused principal amount of the commitments under the Senior Credit Facility. The Senior Credit Facility has a feature whereby at any time, so long as no event of default has occurred and is continuing, the Partnership may request an increase in the Senior Credit Facility of up to $250 million, but no lender has an obligation to increase their respective share of the facility.
	The LIBOR-based interest rate on the Senior Credit Facility averaged 1.41 percent for the year ended December 31, 2014 (2013 – 1.44 percent; 2012 – 1.61 percent). The interest rate was 1.41 percent at December 31, 2014 (December 31, 2013 – 1.42 percent).
	On July 1, 2013, the Partnership entered into a term loan agreement with a syndicate of lenders for a $500 million term loan credit facility (Term Loan Facility). On July 2, 2013, the Partnership borrowed $500 million under the Term Loan Facility, to pay a portion of the purchase price of the 2013 Acquisition, maturing on July 1, 2018. The Term Loan Facility bears interest based, at the Partnership's election, on the LIBOR or the base rate plus, in either case, an applicable margin. The base rate equals the highest of (i) SunTrust Bank's prime rate, (ii) 0.50 percent above the federal funds rate and (iii) 1.00 percent above one-month LIBOR. The applicable margin for the term loan is based on the Partnership's senior debt rating and ranges between 1.125 percent and 2.000 percent for LIBOR borrowings and 0.125 percent and 1.000 percent for base rate borrowings.
	The LIBOR-based interest rate on the Term Loan Facility averaged 1.41 percent for the year ended December 31, 2014 (2013 – 1.43 percent). After hedging activity, the interest rate incurred on the Term Loan Facility averaged 1.82 percent for the year ended December 31, 2014 (2013 – 1.70 percent). Prior to hedging activities, the LIBOR-based interest rate was 1.41 percent at December 31, 2014 (December 31, 2013 – 1.42 percent).
	On October 1, 2014, the Partnership entered into a short-term loan agreement with a member of the syndicate of lenders for a $170 million term loan credit facility (Short-Term Loan Facility). The Partnership borrowed $170 million under the Short-Term Loan Facility to pay a portion of the purchase price of the 2014 Acquisition and to reduce the amount outstanding under our Senior Credit Facility. The outstanding principal bears interest based on the highest of (i) SunTrust Bank's prime rate, (ii) 0.50 percent above the federal funds rate and (iii) 1.00 percent above one-month LIBOR. The Short-Term Loan Facility matures in 364-days.
	The LIBOR-based interest rate on the Short-Term Loan Facility averaged 1.28 percent for the period ended December 31, 2014 and was 1.28 percent at December 31, 2014.
	The Senior Credit Facility, the Term Loan Facilities and Short-Term Loan Facility require the Partnership to maintain a 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)) of no more than 5.00 to 1.00 at the end of each fiscal quarter. The permitted leverage ratio will increase to 5.50 to 1.00 for the fiscal quarter in which a specified material acquisition occurs and for the two fiscal quarters immediately following such acquisition, after which the permitted leverage ratio reverts to 5.00 to 1.00. The leverage ratio was 4.36 to 1.00 as of December 31, 2014. The Senior Credit Facility, the Term Loan Facility and Short-Term Loan Facility contain additional covenants that include restrictions on entering into mergers, consolidations and sales of assets, granting liens, material amendments to the Partnership Agreement, incurrence of additional debt by the Partnership's subsidiaries and distributions to unitholders. Upon any breach of these covenants, amounts outstanding under the Senior Credit Facility, the Term Loan Facility and Short-Term Loan Facility may become immediately due and payable.
	On June 1, 2015, GTN's 5.09 percent unsecured Senior Notes will mature. As market conditions dictate, GTN intends to refinance all or portion of this debt with either fixed-rate or variable rate debt. GTN's Senior Notes provisions contain a covenant that limits total debt to no greater than 70 percent of total capitalization.
	The Series D Senior Notes, which require yearly principal payments until its maturity, are secured by Tuscarora's transportation contracts, supporting agreements and substantially all of Tuscarora's property. The note purchase agreements contain certain provisions that include, among other items, limitations on additional indebtedness and distributions to partners.
	At December 31, 2014, 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 second amended and restated agreement of limited partnership (Partnership Agreement), incurring additional debt and distributions to unitholders.
	The principal repayments required by the Partnership on its debt are as follows:
	(millions of dollars)
	2015	249
	2016	4
	2017	342
	2018	500
	2019	–
	Thereafter	600
		1,695

OTHER_LIABILITIES

OTHER LIABILITIES	12 Months Ended
	Dec. 31, 2014
OTHER LIABILITIES
OTHER LIABILITIES	NOTE 8    OTHER LIABILITIES
		2014	2013
	December 31 (millions of dollars)
	Regulatory liabilities	23	22
	Other liabilities	3	2
		26	24
	The Partnership collects estimated future removal costs related to its transmission and gathering facilities in its current rates and recognizes regulatory liabilities in this respect in the balance sheet. Estimated costs associated with the future removal of transmission and gathering facilities are collected through depreciation as allowed by FERC. These amounts do not represent asset retirement obligations as defined by FASB ASC 410, Accounting for Asset Retirement Obligations.

PARTNERS_EQUITY

PARTNERS' EQUITY	12 Months Ended
	Dec. 31, 2014
PARTNERS' EQUITY
PARTNERS' EQUITY	NOTE 9    PARTNERS' EQUITY
	At December 31, 2014, Partners' equity included 63,561,546 common units (December 31, 2013 – 62,327,766 and 2012 - 53,472,766 common units), representing an effective 98 percent limited partner interest in the Partnership (including 5,797,106 common units held by the General Partner and 11,287,725 common units held indirectly by TransCanada) and an effective two percent general partner interest. In aggregate, the General Partner's interests represent an effective 10.9 percent ownership in the Partnership at December 31, 2014 (December 31, 2013 – 11.1 percent and 2012 – 12.6 percent).
	ATM Equity Issuance Program (ATM Program)
	In August 2014, the Partnership entered into an Equity Distribution Agreement (the EDA) with five different financial institutions (Managers), Pursuant to which the Partnership may from time to time, offer and sell common units having an aggregate offering price of up to $200 million. Sales of such common units will be made by means of ordinary brokers' transactions on the NYSE at market prices, in block transactions or as otherwise agreed upon by one or more of the Managers and the Partnership.
	In 2014, the Partnership issued 1.3 million common units under the ATM Program generating net proceeds of approximately $72 million, plus an additional $1 million from the General Partner's to maintain its effective two percent interest. The commissions to our sales agents were approximately $1 million. The net proceeds were used to finance the 2014 Acquisition (refer to Note 6).
	Equity issuance in connection with the 2013 Acquisition
	On May 22, 2013, the Partnership closed a public offering of 8,855,000 common units, including 1,155,000 common units purchased pursuant to the exercise of the underwriters' option to purchase additional common units, at a price to the public of $43.85 per common unit for gross proceeds of $388 million and net proceeds of $373 million after unit issuance costs. The General Partner maintained its effective two percent general partner interest in the Partnership by contributing $8 million to the Partnership in connection with the offering. (Refer to Note 6).

ACCUMULATED_OTHER_COMPEREHENSI

ACCUMULATED OTHER COMPEREHENSIVE LOSS	12 Months Ended
	Dec. 31, 2014
ACCUMULATED OTHER COMPEREHENSIVE LOSS
ACCUMULATED OTHER COMPEREHENSIVE LOSS	NOTE 10    ACCUMULATED OTHER COMPEREHENSIVE LOSS
	The changes in accumulated other comprehensive loss (AOCL) by components are as follows:
		Cash flow
	(millions of dollars)	hedges
	Balance at December 31, 2011	(1	)
	Other comprehensive loss before reclassifications	–
	Amounts reclassified from AOCL (affected financial charges and other)	–
	Net other comprehensive loss	–
	Balance at December 31, 2012	(1	)
	Other comprehensive loss before reclassifications	–
	Amounts reclassified from AOCL (affected financial charges and other)	–
	Net other comprehensive loss	–
	Balance at December 31, 2013	(1	)
	Other comprehensive loss before reclassifications	(1	)
	Amounts reclassified from AOCL (affected financial charges and other)	–
	Net other comprehensive loss	(1	)
	Balance as of December 31, 2014	(2	)

FINANCIAL_CHARGES_AND_OTHER

FINANCIAL CHARGES AND OTHER	12 Months Ended
	Dec. 31, 2014
FINANCIAL CHARGES AND OTHER
FINANCIAL CHARGES AND OTHER	NOTE 11    FINANCIAL CHARGES AND OTHER
			2014		2013(a)	2012(a)
	Year ended December 31 (millions of dollars)
	Interest expense		48		42	40
	Amortization of debt issue costs		1		1	1
	Net realized loss related to the interest rate swaps and options		2		1	–
	Other		(1	)	–	(1	)
			50		44	40
	(a)	Recast as discussed in Note 2 and Note 6.

NET_INCOME_PER_COMMON_UNIT

NET INCOME PER COMMON UNIT	12 Months Ended
	Dec. 31, 2014
NET INCOME PER COMMON UNIT
NET INCOME PER COMMON UNIT	NOTE 12    NET INCOME PER COMMON UNIT
	Net income per common unit is computed by dividing net income attributable to controlling interests, after deduction of the General Partner's allocation and net income attributed to GTN's and Bison's former parent, by the weighted average number of common units outstanding. The General Partner's allocation is equal to 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. In the year ended December 31, 2014, incentive distributions allocated to the General Partner were $1 million. No incentive distributions were allocated to the General Partner in the years ended December 31, 2013 and 2012.
	Net income per common unit was determined as follows:
			2014	2013(a)		2012(a)
	(millions of dollars, except per common unit amounts)
	Net income attributable to controlling interests		172	155		192
	Net income attributed to GTN's and Bison's former parent(b)		–	(26	)	(55	)
	Net income allocated to controlling interests(b)		172	129		137
	Net income allocated to General Partner, including incentive distribution rights (IDRs)(c)		4	3		3
	Net income allocable to common units		168	126		134
	Weighted average common units outstanding (millions) – basic and diluted		62.7	58.9		53.5
	Net income per common unit – basic and diluted		$	$		$
			2.67	2.13		2.51
	(a)	Recast as discussed in Note 2 and Note 6.
	(b)	Net income allocated to controlling interests excludes net income attributed to GTN's and Bison's former parent as it was allocated to TransCanada and was not allocable to either the general partner or common units.
	(c)	In the calculation of basic and diluted net income per common unit, the net income allocated to the General Partner includes IDRs pertaining to the current reporting period, but declared and paid in the subsequent period.

CASH_DISTRIBUTIONS

CASH DISTRIBUTIONS	12 Months Ended
	Dec. 31, 2014
CASH DISTRIBUTIONS
CASH DISTRIBUTIONS	NOTE 13    CASH DISTRIBUTIONS
	The Partnership makes cash distributions to its partners with respect to each calendar quarter within 45 days after the end of each quarter. Distributions are based on Available Cash, as defined in the Partnership Agreement, which includes all cash and cash equivalents of the Partnership and working capital borrowings less reserves established by the General Partner. The Partnership declared a quarterly distribution of $0.81 per common unit based on the first quarter results of 2014 and $0.84 per common unit for the remainder of the quarters of 2014. The quarterly distribution occurs if there is, and to the extent of, sufficient Available Cash.
	As an incentive, the General Partner's percentage interest in quarterly distributions is increased after certain specified target levels are met. Currently, the combined general partner interest and incentive distribution interest payable to the General Partner is 15 percent to a maximum of 25 percent of all quarterly distributions of Available Cash that exceed target levels of $0.81 and $0.88, respectively, per common unit.
	For the year ended December 31, 2014, the Partnership distributed $3.30 per common unit (2013 – $3.18 per common unit; 2012 – $3.10 per common unit) for a total of $212 million (2013 – $188 million; 2012 – $169 million). The distributions paid for the year ended December 31, 2014 included incentive distributions to the General Partner of $1 million. There were no incentive distributions paid to the General Partner in the years ended December 31, 2013 and 2012. Partnership income attributable to controlling interests is allocated to the General Partner and the limited partners in accordance with their respective partnership percentages, after giving effect to any priority income allocations for incentive distributions that are allocated 100 percent to the General Partner.

CHANGE_IN_OPERATING_WORKING_CA

CHANGE IN OPERATING WORKING CAPITAL	12 Months Ended
	Dec. 31, 2014
CHANGE IN OPERATING WORKING CAPITAL
CHANGE IN OPERATING WORKING CAPITAL	NOTE 14    CHANGE IN OPERATING WORKING CAPITAL
			2014	2013(a)		2012(a)
	Year Ended December 31 (millions of dollars)
	Change in accounts receivable and other		2	1		2
	Change in accounts payable and accrued liabilities		4	(9	)	(2	)
	Change in accounts payable to affiliates(b)		11	(2	)	–
	Change in accrued interest		–	2		–
	Change in operating working capital		17	(8	)	–
	(a)	Recast as discussed in Note 2 and Note 6.
	(b)	Excludes Carty Lateral accrual of $25 million at December 31, 2013.

TRANSACTIONS_WITH_MAJOR_CUSTOM

TRANSACTIONS WITH MAJOR CUSTOMERS	12 Months Ended
	Dec. 31, 2014
TRANSACTIONS WITH MAJOR CUSTOMERS
TRANSACTIONS WITH MAJOR CUSTOMERS	NOTE 15    TRANSACTIONS WITH MAJOR CUSTOMERS
	The following table shows revenues from the Partnership's major customers comprising more than 10 percent of the Partnership's total revenues for the years ended December 31, 2014, 2013 and 2012:
			2014	2013(a)	2012(a)
	Year Ended December 31 (millions of dollars)
	Anadarko Energy Services Company (Anadarko)		48	48	48
	Pacific Gas and Electric Company (Pacific Gas)		45	46	47
	(a)	Recast as discussed in Note 2 and Note 6.
	At December 31, 2014 and 2013, Anadarko and Pacific Gas each owed the Partnership approximately $4 million, which is greater than 10% of Accounts receivable and other.

RELATED_PARTY_TRANSACTIONS

RELATED PARTY TRANSACTIONS	12 Months Ended
	Dec. 31, 2014
RELATED PARTY TRANSACTIONS
RELATED PARTY TRANSACTIONS	NOTE 16    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. Total costs charged to the Partnership by the General Partner were $3 million for the year ended December 31, 2014 (2013 and 2012 – $3 million).
	As operator, TransCanada's subsidiaries provide capital and operating services to GTN, Northern Border, Bison, Great Lakes, North Baja and Tuscarora (together, "our pipeline systems"). TransCanada's subsidiaries incur costs on behalf of our pipeline systems, including, but not limited to, employee salary and benefit costs, and property and liability insurance costs.
	Capital and operating costs charged to our pipeline systems for the years ended December 31, 2014, 2013 and 2012 by TransCanada's subsidiaries and amounts payable to TransCanada's subsidiaries at December 31, 2014 and 2013 are summarized in the following tables:
			2014	2013	2012
	Year ended December 31 (millions of dollars)
	Capital and operating costs charged by TransCanada's subsidiaries to:
		GTN(a)(b)	30	28	29
		Northern Border(a)	35	30	31
		Bison(a)(b)(c)	6	5	6
		Great Lakes(a)	30	31	33
		North Baja	5	4	4
		Tuscarora	4	4	4
	Impact on the Partnership's net income attributable to controlling interests:
		GTN(b)	19	19	19
		Northern Border	16	14	14
		Bison(b)(c)	4	4	4
		Great Lakes	13	14	15
		North Baja	4	4	4
		Tuscarora	4	4	4
			2014	2013
	December 31 (millions of dollars)
	Amount payable to TransCanada's subsidiaries for costs charged in the year by:
		GTN(a)	10	3
		Northern Border(a)	10	3
		Bison(a)	2	–
		Great Lakes(a)	9	3
		North Baja	1	1
		Tuscarora	1	–
	(a)	Represents 100 percent of the costs.
	(b)	Recast as discussed in Note 2 and Note 6.
	(c)	In 2014, the Partnership acquired remaining 30 percent interest in Bison. See discussion in Note 6.
	Great Lakes' earns transportation revenues from TransCanada and its affiliates under contracts, some of which are provided at discounted rates and some at maximum recourse rates. Great Lakes earned $71 million of transportation revenues under these contracts in 2014 (2013 – $68 million; 2012 – $77 million). This amount represents 49 percent of total revenues earned by Great Lakes in 2014 (2013 – 55 percent; 2012 – 42 percent). Great Lakes also earned $2 million in affiliated rental revenue in 2014 (2013 and 2012 – $1 million).
	Revenue from TransCanada and its affiliates of $34 million is included in the Partnership's equity earnings from Great Lakes in 2014 (2013 – $32 million; 2012 – $36 million). At December 31, 2014, $15 million was included in Great Lakes' receivables in regards to the transportation contracts with TransCanada and its affiliates (2013 – $11 million).
	Effective November 1, 2014, Great Lakes executed contracts with its affiliate, ANR Pipeline Company (ANR) to provide seasonal firm service between Michigan and Wisconsin. These contracts were at the maximum FERC authorized rate and were intended to replace historical contracts. On December 3, 2014, the FERC accepted and suspended Great Lakes' tariff records to become effective May 3, 2015, subject to refund. On January 2, 2015, Great Lakes submitted a request for rehearing and clarification with FERC. On February 2, 2015 FERC issued an Order granting rehearing to allow for additional time for FERC to consider the request. Until Great Lakes obtains clarification from FERC or a settlement is reached and approved, it is providing service to ANR under multiple service agreements and rates. Great Lakes has deferred $9.4 million of revenue under such agreements that may not be collected.
	At December 31, 2013, the Partnership accrued $25 million of additional consideration in accordance with the 2013 Acquisition with respect to Carty Lateral. This amount was payable to a subsidiary of TransCanada and was included in accounts payable to affiliates as of December 31, 2013 (refer to Note 6). This amount was paid in full in April 2014.
	Bison's former parent made an equity contribution to Bison of $18 million in the second quarter of 2013. This amount represents the former parent's 75 percent share of a $24 million cash call from Bison to repay inter-affiliate debt primarily related to pipeline construction costs, including reclamation and restoration work.
	Effective October 1, 2013, GTN and Bison participated in the Partnership's cash management program. Prior to this, GTN and Bison were part of TransCanada's cash management program. This program matches short-term cash surpluses and borrowing requirements of participating subsidiaries, thus minimizing total borrowing from outside sources. Funds advanced under the program are considered to be a loan, accruing interest and repayable on demand. GTN and Bison will receive interest on funds advanced to the Partnership at the rate of interest earned by the Partnership on its short-term cash investments and will pay interest on funds advanced from the Partnership based on the Partnership's short-term borrowing costs. At December 31, 2014 and 2013, GTN and Bison did not have any demand loan receivable from an affiliate or a demand loan payable to an affiliate.

QUARTERLY_FINANCIAL_DATA_unaud

QUARTERLY FINANCIAL DATA (unaudited)	12 Months Ended
	Dec. 31, 2014
QUARTERLY FINANCIAL DATA (unaudited)
QUARTERLY FINANCIAL DATA (unaudited)	NOTE 17    QUARTERLY FINANCIAL DATA (unaudited)
	The following sets forth selected unaudited financial data for the four quarters in 2014 and 2013:
			31-Mar	30-Jun	30-Sep	31-Dec
	Quarter ended (millions of dollars except per common unit amounts)
	2014
	Transmission revenues		87	82	80	87
	Equity earnings		33	18	15	22
	Net income		67	45	39	53
	Net income attributable to controlling interests		57	37	31	47
	Net income per common unit		$	$	$	$
			0.90	0.58	0.48	0.71
	Cash distribution paid		52	52	54	54
	2013
	Transmission revenues(a)		86	82	85	88
	Equity earnings(a)		18	15	15	19
	Net income(a)		53	42	46	50
	Net income attributable to controlling interests(a)		43	34	37	41
	Net income per common unit		$	$	$	$
			0.52	0.40	0.58	0.63
	Cash distributions paid		43	43	52	52
	(a)	Recast as discussed in Note 2 and Note 6.

FAIR_VALUE_MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2014
FAIR VALUE MEASUREMENTS
FAIR VALUE MEASUREMENTS	NOTE 18    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 input 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 long-term debt is estimated by discounting the future cash flows of each instrument at estimated current borrowing rates. The fair value of interest rate derivatives is calculated using the income approach which uses period-end market rates and applies a discounted cash flow valuation model.
	The estimated fair value of the Partnership's long-term debt as at December 31, 2014 and 2013 are as follows:
	2014		2013
			Carrying Value	Fair Value	Carrying Value	Fair Value
	December 31 (millions of dollars)
	Senior Credit Facility due 2017		330	330	380	380
	Term Loan Facility due 2018		500	500	500	500
	Short-Term Loan Facility due 2015		170	170	–	–
	4.65% Senior Notes due 2021		350	375	349	353
	5.09% Unsecured Senior Notes due 2015		75	76	75	79
	5.29% Unsecured Senior Notes due 2020		100	111	100	106
	5.69% Unsecured Senior Notes due 2035		150	168	150	154
	3.82% Series D Senior Notes due 2017		20	21	24	25
			1,695	1,751	1,578	1,597
	Long-term debt is recorded at amortized cost and classified in Level II of the fair value hierarchy for fair value disclosure purposes. Interest rate derivative assets and liabilities are classified in Level II for all periods presented where the fair value is determined by using valuation techniques that refer to observable market data or estimated market prices.
	Market risk is the risk that changes in market interest rates may result in fluctuations in the fair values or cash flows of financial instruments. The Partnership's floating rate debt is subject to LIBOR benchmark interest rate risk. The Partnership uses interest rate derivatives to manage its exposure to interest rate risk. We regularly assess the impact of interest rate fluctuations on future cash flows and evaluate hedging opportunities to mitigate our interest rate risk.
	The interest rate swaps are structured such that the cash flows of the derivative instruments match those of the variable rate of interest on the Term Loan Facility. The Partnership hedged interest payments on $150 million of variable-rate Term Loan Facility with interest rate swaps effective September 3, 2013 and maturing July 1, 2018, at a weighted average fixed interest rate of 2.79 percent. At December 31, 2014, the fair value of the interest rate swaps accounted for as cash flow hedges was a liability of $1 million (both on a gross and net basis) (December 31, 2013 – less than $1 million; 2012 – nil). In 2014, the Partnership did not record any amounts in net income related to ineffectiveness for interest rate hedges. The change in fair value of interest rate derivative instruments recognized in other comprehensive income was a loss of $1 million for the year ended December 31, 2014 (2013 – less than $1 million; 2012 – nil). In 2014, the net realized loss related to the interest rate swaps was $2 million and was included in financial charges and other (2013 – $1 million; 2012 – nil).
	The Partnership has no master netting agreements, however, contracts contain provisions with rights of offset. The Partnership has elected to present the fair value of derivative instruments with the right to offset on a gross basis in the balance sheet. Had the Partnership elected to present these instruments on a net basis, there would be no effect on the consolidated balance sheet as of December 31, 2014 and 2013.
	Counterparty credit risk represents the financial loss that the Partnership would experience if a counterparty to a financial instrument failed to meet its obligations in accordance with the terms and conditions of the financial instruments with the Partnership. Our maximum counterparty credit exposure with respect to financial instruments at the balance sheet date consists primarily of the carrying amount, which approximates fair value, of non-derivative financial assets, such as accounts receivable, as well as the fair value of derivative financial assets. We review our accounts receivable regularly and record allowances for doubtful accounts using the specific identification method. At December 31, 2014, we had not incurred any significant credit losses and had no significant amounts past due or impaired. At December 31, 2014, the Partnership's maximum counterparty credit exposure consisted of accounts receivable of $35 million (2013 – $37 million).

ACCOUNTS_RECEIVABLE_AND_OTHER

ACCOUNTS RECEIVABLE AND OTHER	12 Months Ended
	Dec. 31, 2014
ACCOUNTS RECEIVABLE AND OTHER
ACCOUNTS RECEIVABLE AND OTHER	NOTE 19    ACCOUNTS RECEIVABLE AND OTHER
		2014	2013
	December 31 (millions of dollars)
	Trade accounts receivable, net of allowance of nil	30	33
	Accounts receivable from affiliates	1	–
	Other	4	4
		35	37

REGULATORY_MATTERS

REGULATORY MATTERS	12 Months Ended
	Dec. 31, 2014
REGULATORY MATTERS
REGULATORY MATTERS	NOTE 20    REGULATORY MATTERS
	North Baja – On January 6, 2014, FERC approved North Baja's application to temporarily abandon compression associated with the original design of its pipeline system. This temporary abandonment will preserve replacement options while reducing maintenance requirements and related expenses without any reduction in capacity or impact to existing firm transportation service.

CONTINGENCIES

CONTINGENCIES	12 Months Ended
	Dec. 31, 2014
CONTINGENCIES
CONTINGENCIES	NOTE 21    CONTINGENCIES
	In December 2009, PacifiCorp filed suit against GTN and Northwest Pipeline in Oregon State Court for approximately $7 million for alleged damage to equipment at its natural gas generating facility in Hermiston, Oregon. Upon GTN motion, the case was removed to the U.S. District Court for the District of Oregon and was scheduled for trial in March 2014. However, in February 2014, the parties settled all claims in the case. The impact on the Partnership's consolidated results was not material.

SUBSEQUENT_EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2014
SUBSEQUENT EVENTS
SUBSEQUENT EVENTS	NOTE 22    SUBSEQUENT EVENTS
	Management of the Partnership has reviewed subsequent events through February 27, 2015, the date the financial statements were issued, and concluded there were no events or transactions during this period that would require recognition or disclosure in the consolidated financial statements other than what is disclosed here and/or those already disclosed in the preceding notes.
	On January 22, 2015, the board of directors of our General Partner declared the Partnership's fourth quarter 2014 cash distribution in the amount of $0.84 per common unit. The fourth quarter cash distribution, which was paid on February 13, 2015 to unitholders of record as of February 3, 2015, totaled $55 million and was paid in the following manner: $54 million to common unitholders (including $5 million to the General Partner as holder of 5,797,106 common units and $9 million to another subsidiary of TransCanada as holder of 11,287,725 common units) and $1 million to the General Partner in respect of its effective two percent general partner interest, which included IDRs of nil million.
	GTN declared its fourth quarter 2014 distribution of $31 million on January 8, 2015, of which the Partnership received its 70 percent share or $21 million. The distribution was paid on February 2, 2015.
	Northern Border declared its fourth quarter 2014 distribution of $43 million on January 12, 2015, of which the Partnership received its 50 percent share or $21 million. The distribution was paid on February 2, 2015.
	Great Lakes declared its fourth quarter 2014 distribution of $17 million on January 8, 2015, of which the Partnership received its 46.45 percent share or $8 million. The distribution was paid on February 2, 2015.
	On February 24, 2015, the Partnership entered into an agreement to acquire the remaining 30 percent interest in GTN from TransCanada for $446 million comprised of $253 million in cash, the assumption of $98 million in proportional GTN debt and the issuance of $95 million of new Class B units to TransCanada. The Partnership plans to fund the cash portion of the transaction through a combination of debt and common equity. The Class B units will be entitled to distribution based on 30 percent of GTN's annual distributions as follows: i) for the first five years, 100 percent of distributions above $20 million; and ii) for subsequent years, 25 percent of distributions above $20 million. The transaction is expected to close on April 1, 2015.
	The transaction was approved by the Board of Directors of the General Partner, based on approval and recommendation from the Board's conflicts committee which is comprised entirely of independent directors.

SIGNIFICANT_ACCOUNTING_POLICIE1

SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2014
SIGNIFICANT ACCOUNTING POLICIES
Basis of Presentation	(a)    Basis of Presentation
	The Partnership consolidates its investments in GTN, Bison, North Baja and Tuscarora, over which it is able to exercise control. To the extent there are interests owned by other parties, these interests are included in non-controlling interests. The Partnership uses the equity method of accounting for its investments in Northern Border and Great Lakes, over which it is able to exercise significant influence.
	On October 1, 2014, the Partnership acquired the remaining 30 percent interest in Bison from a subsidiary of TransCanada (the 2014 Acquisition), which resulted in Bison being wholly-owned by the Partnership. Prior to this transaction, the remaining 30 percent interest held by a subsidiary of TransCanada was reflected as non-controlling interest in the consolidated financial statements. The 2014 Acquisition of this already-consolidated entity was accounted for as a transaction between entities under common control, similar to a pooling of interests, whereby the acquired interest was recorded at TransCanada's carrying value and the total excess purchase price paid was recorded as a reduction in Partners' Equity. Refer to Note 6 for additional disclosure regarding the 2014 Acquisition.
	On July 1, 2013, the Partnership acquired a 45 percent membership interest in each of GTN and Bison (the 2013 Acquisition) from subsidiaries of TransCanada increasing the Partnership's ownership in each of GTN and Bison to 70 percent. The 2013 Acquisition was accounted for as a transaction between entities under common control, similar to a pooling of interests, whereby the assets and liabilities of GTN and Bison were recorded at TransCanada's carrying value and the Partnership's historical financial information, except net income per common unit, was recast to consolidate GTN and Bison for all periods presented. Refer to Note 6 for additional disclosure regarding the 2013 Acquisition.
Use of Estimates	(b)    Use of Estimates
	The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Although management believes these estimates are reasonable, actual results could differ from these estimates.
Cash and Cash Equivalents	(c)    Cash and Cash Equivalents
	The Partnership's cash and cash equivalents consist of cash and highly liquid short-term investments with original maturities of three months or less and are recorded at cost, which approximates fair value.
Trade Accounts Receivable	(d)    Trade Accounts Receivable
	Trade accounts receivable are recorded at the invoiced amount and do not bear interest. We review our accounts receivable regularly and record allowances for doubtful accounts using the specific identification method.
Inventories
	(e)    Inventories
	Inventories primarily consist of materials and supplies and are carried at the lower of weighted average cost or market.
Plant, Property and Equipment	(f)    Plant, Property and Equipment
	Plant, property and equipment are stated at original cost. Costs of restoring the land above and around the pipeline are capitalized to pipeline facilities and depreciated over the remaining life of the related pipeline facilities. Pipeline facilities and compression equipment have an estimated useful life of 20 to 77 years and metering and other equipment ranges from 5 to 77 years. Depreciation is calculated on a straight-line composite basis over the assets' estimated useful lives. Repair and maintenance costs are expensed as incurred. Costs that are considered a betterment are capitalized.
	An allowance for funds used during construction, using the rate of return on rate base approved by the Federal Energy Regulatory Commission (FERC), is capitalized and included in the cost of plant, property and equipment. Amounts included in construction work in progress are not amortized until transferred into service.
Impairment of Equity Investments	(g)    Impairment of Equity Investments
	We review our equity method investments when a significant event or change in circumstances has occurred that may have an adverse effect on the fair value of each investment. When such events or changes occur, we compare the estimated fair value to the carrying value of the related investment. We also perform this evaluation every reporting period for each investment for which the carrying value has exceeded the fair value in the prior period. We calculate the estimated fair value of an investment in an equity method investee using an income approach and market approach. The development of fair value estimates requires significant judgment including estimates of future cash flows, which is dependent on internal forecasts, estimates of the long-term rate of growth for the investee, estimates of the useful life over which cash flows will occur, and determination of weighted average cost of capital. The estimates used to calculate the fair value of an investee can change from year to year based on operating results and market conditions. Changes in these estimates and assumptions could materially affect the determination of fair value and our assessment as to whether an investment in an equity method investee has suffered an impairment.
	If the estimated fair value of an investment is less than its carrying value, we are required to determine if the decline in fair value is other than temporary. This determination considers the aforementioned valuation methodologies, the length of time and the extent to which fair value has been less than carrying value, the financial condition and near-term prospects of the investee, including any specific events which may influence the operations of the investee, the intent and ability of the holder to retain its investment in the investee for a period of time sufficient to allow for any anticipated recovery in market value, and other facts and circumstances. If the fair value of an investment is less than its carrying value and the decline in value is determined to be other than temporary, we record an impairment charge.
Impairment of Long-lived Assets	(h)    Impairment of Long-lived Assets
	The Partnership reviews long-lived assets, such as plant, property and equipment for impairment whenever events or changes in circumstances indicate the carrying value may not be recoverable. If the total of the estimated undiscounted future cash flows is less than the carrying value of the assets, an impairment loss is recognized for the excess of the carrying value over the fair value of the assets.
Partners' Equity	(i)    Partners' Equity
	Costs incurred in connection with the issuance of units are deducted from the proceeds received.
Revenue Recognition	(j)    Revenue Recognition
	Transmission revenues are recognized in the period in which the service is provided. When a rate case is pending final FERC approval, a portion of the revenue collected is subject to possible refund. As of December 31, 2014, 2013 and 2012, the Partnership has not recognized any transmission revenue that is subject to possible refund.
Income Taxes	(k)    Income Taxes
	The Partnership is not subject to federal or state income tax. The tax effect of the Partnership's activities accrues to its partners. The Partnership's taxable income or loss, which may vary substantially from the net income or loss reported in the consolidated statement of income, is includable in the federal income tax returns of each partner. The aggregate difference in the basis of the Partnership's net assets for financial and income tax purposes cannot be readily determined because all information regarding each partner's tax attributes related to the partnership is not available.
	As a result of the recast of the Partnership's historical financial information (refer to Note 2 (a)), the Partnership included income taxes in its consolidated financial statements for the year ended December 31, 2011. Those income taxes relate to GTN for the periods prior to April 1, 2011. GTN is no longer subject to income taxes and settled all current and deferred income tax balances pursuant to GTN's tax-sharing agreement with TransCanada PipeLine USA Ltd. upon conversion to an LLC on April 1, 2011. GTN used the Asset and Liability method of accounting for income taxes for the periods prior to April 1, 2011.
Acquisitions and Goodwill	(l)    Acquisitions and Goodwill
	The Partnership accounts for business acquisitions from third parties using the acquisition method of accounting and, accordingly, the assets and liabilities of the acquired entities are recorded at their estimated fair values at the date of acquisition. The excess of the purchase price over the fair value of net assets acquired is attributed to goodwill. Goodwill is not amortized and is tested on an annual basis for impairment or more frequently if any indicators of impairment are evident. The Partnership initially assesses qualitative factors to determine whether events or changes in circumstances indicate that the goodwill might be impaired. If the Partnership does not conclude that it is more likely than not that fair value of the reporting unit is greater than its carrying value, the first step of the two-step impairment test is performed by comparing the fair value of the reporting unit to its book value, which includes goodwill. If the fair value is less than book value, an impairment is indicated and a second step is performed to measure the amount of the impairment. In the second step, the implied fair value of goodwill is calculated by deducting the recognized amounts of all tangible and intangible net assets of the reporting unit from the fair value determined in the initial assessment. If the carrying value of goodwill exceeds the calculated implied fair value of goodwill, an impairment charge is recorded.
	The Partnership accounts for business acquisitions between itself and TransCanada as transactions between entities under common control. Using this approach, the assets and liabilities of the acquired entities are recorded at TransCanada's carrying value. In the event recasting is required, the Partnership's historical financial information will be recast, except net income per common unit, to include the acquired entities for all periods presented. If the fair market value paid for the acquired entities is greater than the recorded net assets of the acquired entities, the excess purchase price paid is recorded as a reduction in Partners' Equity. Similarly, if the fair market value paid for the acquired entities is less than the recorded net assets of the acquired entities, the excess of assets acquired is recorded as an increase in Partners' Equity.
Fair Value Measurements	(m)    Fair Value Measurements
	For cash and cash equivalents, receivables, accounts payable and certain accrued expenses, the carrying amount approximates fair value due to the short maturities of these instruments. For long-term debt instruments and the interest rate swap agreements, fair value is estimated based upon market values (if applicable) or on the current interest rates available to us for debt with similar terms and remaining maturities. Considerable judgment is required in developing these estimates.
Derivative Financial Instruments and Hedging Activities	(n)    Derivative Financial Instruments and Hedging Activities
	The Partnership recognizes all derivative instruments as either assets or liabilities in the balance sheet at their respective fair values. For derivatives designated in hedging relationships, changes in the fair value are either offset through earnings against the change in fair value of the hedged item attributable to the risk being hedged or recognized in accumulated other comprehensive income, to the extent the derivative is effective at offsetting the changes in cash flows being hedged until the hedged item affects earnings.
	The Partnership only enters into derivative contracts that it intends to designate as a hedge of a forecasted transaction or the variability of cash flows to be received or paid related to a recognized asset or liability (cash flow hedge). For all hedging relationships, the Partnership formally documents the hedging relationship and its risk management objective and strategy for undertaking the hedge, the hedging instrument, the hedged transaction, the nature of the risk being hedged, how the hedging instrument's effectiveness in offsetting the hedged risk will be assessed prospectively and retrospectively, and a description of the method used to measure ineffectiveness. The Partnership also formally assesses, both at the inception of the hedging relationship and on an ongoing basis, whether the derivatives that are used in hedging relationships are highly effective in offsetting changes in cash flows of hedged transactions. For derivative instruments that are designated and qualify as part of a cash flow hedging relationship, the effective portion of the gain or loss on the derivative is reported as a component of other comprehensive income and reclassified into earnings in the same period or periods during which the hedged transaction affects earnings. Gains and losses on the derivative representing either hedge ineffectiveness or hedge components excluded from the assessment of effectiveness are recognized in current earnings.
	The Partnership discontinues hedge accounting prospectively when it determines that the derivative is no longer effective in offsetting cash flows attributable to the hedged risk, the derivative expires or is sold, terminated, or exercised, the cash flow hedge is de-designated because a forecasted transaction is not probable of occurring, or management determines to remove the designation of the cash flow hedge.
	In all situations in which hedge accounting is discontinued and the derivative remains outstanding, the Partnership continues to carry the derivative at its fair value on the balance sheet and recognizes any subsequent changes in its fair value in earnings. When it is probable that a forecasted transaction will not occur, the Partnership discontinues hedge accounting and recognizes immediately in earnings gains and losses that were accumulated in other comprehensive income related to the hedging relationship.
Asset Retirement Obligation	(o)    Asset Retirement Obligation
	The Partnership recognizes the fair value of a liability for asset retirement obligations in the period in which it is incurred, when a legal obligation exists and a reasonable estimate of fair value can be made. The fair value is added to the carrying amount of the associated asset and the liability is accreted through charges to operating expenses.
	The scope and timing of asset retirements related to natural gas pipelines is indeterminable. As a result, the Partnership has recorded no asset retirement obligations as of December 31, 2014 and 2013.
Government Regulation	(p)    Government Regulation
	The Partnership's subsidiaries are subject to regulation by FERC. Under regulatory accounting principles, certain assets or liabilities that result from the regulated ratemaking process may be recorded that would not be recorded under GAAP for non-regulated entities. The timing of recognition of certain revenues and expenses in our regulated business may differ from that otherwise expected under GAAP to appropriately reflect the economic impact of the regulators' decisions regarding revenues and rates. The Partnership regularly evaluates the continued applicability of regulatory accounting, considering such factors as regulatory changes, the impact of competition, and the ability to recover regulatory assets. The Partnership had no material regulatory assets as of December 31, 2014 and 2013. Regulatory liabilities are included in other long-term liabilities (refer to Note 8). Allowance for funds used during construction is capitalized and included in plant, property and equipment.
Debt Issuance Costs	(q)    Debt Issuance Costs
	Costs related to the issuance of debt are deferred and amortized using the effective interest rate method over the term of the related debt.

ORGANIZATION_Tables

ORGANIZATION (Tables)	12 Months Ended
	Dec. 31, 2014
ORGANIZATION
Schedule of ownership interests in natural gas pipeline systems	Pipeline	Length	Description	Ownership
	Gas Transmission Northwest LLC (GTN)	1,353 miles	Extends between an interconnection near Kingsgate, British Columbia, Canada at the Canadian border to a point near Malin, Oregon at the California border and delivers natural gas to the Pacific Northwest and to California. TransCanada owns the remaining 30 percent of GTN (See Note 22 – Subsequent Events).	70 percent
	Northern Border Pipeline Company (Northern Border)	1,408 miles	Extends between the Canadian border near Port of Morgan, Montana to a terminus near North Hayden, Indiana, south of Chicago. Northern Border is capable of receiving natural gas from Canada, the Williston Basin and Rocky Mountain Basin. ONEOK Partners, L.P. owns the remaining 50 percent of Northern Border.	50 percent
	Bison Pipeline LLC (Bison)	303 miles	Extends from a location near Gillette, Wyoming to Northern Border's pipeline system in North Dakota. Bison transports natural gas from the Powder River Basin to Midwest markets.	100 percent
	Great Lakes Gas Transmission Limited Partnership (Great Lakes)	2,115 miles	Connects with the TransCanada Mainline at the Canadian border near Emerson, Manitoba, Canada and St. Clair, Michigan, near Detroit. Great Lakes is a bi-directional pipeline that can receive and deliver natural gas at multiple points along its system. TransCanada owns the remaining 53.55 percent of Great Lakes.	46.45 percent
	North Baja Pipeline, LLC (North Baja)	86 miles	Extends between an interconnection with the El Paso Natural Gas Company pipeline near Ehrenberg, Arizona and an interconnection with a natural gas pipeline near Ogilby, California on the Mexican border. North Baja is a bi-directional pipeline.	100 percent
	Tuscarora Gas Transmission Company (Tuscarora)	305 miles	Extends between the GTN pipeline near Malin, Oregon to its terminus near Reno, Nevada and delivers natural gas in northeastern California and northwestern Nevada.	100 percent

INVESTMENTS_IN_UNCONSOLIDATED_1

INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Tables)	12 Months Ended
	Dec. 31, 2014
INVESTMENTS IN UNCONSOLIDATED AFFILIATES
Schedule of investments in unconsolidated affiliates
	Equity Earnings from Unconsolidated Affiliates					Investment in Unconsolidated Affiliates
	Year ended December 31					December 31
	Ownership
	Interest at
	(millions of dollars)	December 31, 2014		2014		2013		2012	2014	2013
	Northern Border(a)		50%		69		64		72	505	523
	Great Lakes		46.45%		19		3		27	672	672
					88		67		99	1,177	1,195
	(a)	Equity earnings from Northern Border is net of the 12-year amortization of a $10 million transaction fee paid to the operator of Northern Border at the time of the Partnership's additional 20 percent acquisition in April 2006.
Northern Border
Investments in unconsolidated affiliates
Summarized financial information for equity investees
	December 31 (millions of dollars)			2014		2013
	Assets
	Cash and cash equivalents			41		27
	Other current assets			34		34
	Plant, property and equipment, net			1,163		1,197
	Other assets			34		33
				1,272		1,291
	Liabilities and Partners' Equity
	Current liabilities			64		51
	Deferred credits and other			22		19
	Long-term debt			411		411
	Partners' equity
		Partners' capital		777		812
		Accumulated other comprehensive loss		(2	)	(2	)
				1,272		1,291
	Year ended December 31 (millions of dollars)		2014		2013		2012
	Transmission revenues		293		286		311
	Operating expenses		(72	)	(75	)	(79	)
	Depreciation		(59	)	(58	)	(63	)
	Financial charges and other		(22	)	(23	)	(24	)
	Net income		140		130		145
Great Lakes
Investments in unconsolidated affiliates
Summarized financial information for equity investees
	December 31 (millions of dollars)		2014		2013
	Assets
	Current assets		66		52
	Plant, property and equipment, net		748		771
			814		823
	Liabilities and Partners' Equity
	Current liabilities		38		28
	Long-term debt, including current maturities		316		335
	Partners' equity		460		460
			814		823
	Year ended December 31 (millions of dollars)		2014		2013		2012
	Transmission revenues		146		124		182
	Operating expenses		(53	)	(60	)	(66	)
	Depreciation		(28	)	(31	)	(31	)
	Financial charges and other		(25	)	(27	)	(28	)
	Net income		40		6		57

PLANT_PROPERTY_AND_EQUIPMENT_T

PLANT, PROPERTY AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2014
PLANT, PROPERTY AND EQUIPMENT
Schedule of plant, property and equipment
	2014				2013
	December 31 (millions of dollars)
		Cost	Accumulated		Net Book	Cost	Accumulated		Net Book
			Depreciation		Value		Depreciation		Value
	Pipeline	2,038	(574	)	1,464	2,045	(522	)	1,523
	Compression	514	(126	)	388	520	(120	)	400
	Metering and other	145	(37	)	108	146	(32	)	114
	Construction in progress	8	–		8	5	–		5
		2,705	(737	)	1,968	2,716	(674	)	2,042

ACQUISITIONS_Tables

ACQUISITIONS (Tables)	12 Months Ended
	Dec. 31, 2014
Bison
Acquisition
Schedule of purchase price
	(millions of dollars)
	Total cash consideration	217
	TransCanada's carrying value of non-controlling interest at October 1, 2014	188
	Excess purchase price	29
GTN and Bison
Acquisition
Schedule of purchase price
	(millions of dollars)
	Current assets	67
	Property, plant and equipment, net	1,792
	Other assets	1
	Current liabilities	(20	)
	Other liabilities	(21	)
	Long-term debt	(325	)
		1,494
	Non-controlling interest	(448	)
	Carrying value of pre-existing 25% interest in each of GTN and Bison	(374	)
	Carrying value of acquired 45% interest in each of GTN and Bison	672
	Excess purchase price over net assets acquired (includes Carty Lateral consideration)	274
	Total cash consideration including $25 million Carty Lateral consideration	946

CREDIT_FACILITIES_SHORTTERM_LO1

CREDIT FACILITIES, SHORT-TERM LOAN FACILITY AND LONG-TERM DEBT (Tables)	12 Months Ended
	Dec. 31, 2014
CREDIT FACILITIES, SHORT-TERM LOAN FACILITY AND LONG-TERM DEBT
Schedule of credit facilities, short-term loan facility and long-term debt
		2014	2013
	December 31 (millions of dollars)
	Senior Credit Facility due 2017	330	380
	Term Loan Facility due 2018	500	500
	Short-Term Loan Facility due 2015	170	–
	4.65% Unsecured Senior Notes due 2021	350	349
	5.09% Unsecured Senior Notes due 2015	75	75
	5.29% Unsecured Senior Notes due 2020	100	100
	5.69% Unsecured Senior Notes due 2035	150	150
	3.82% Series D Senior Notes due 2017	20	24
		1,695	1,578
	Less: current portion	249	3
		1,446	1,575
Schedule of principal repayments required on debt
	(millions of dollars)
	2015	249
	2016	4
	2017	342
	2018	500
	2019	–
	Thereafter	600
		1,695

OTHER_LIABILITIES_Tables

OTHER LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2014
OTHER LIABILITIES
Schedule of other liabilities
		2014	2013
	December 31 (millions of dollars)
	Regulatory liabilities	23	22
	Other liabilities	3	2
		26	24

ACCUMULATED_OTHER_COMPEREHENSI1

ACCUMULATED OTHER COMPEREHENSIVE LOSS (Tables)	12 Months Ended
	Dec. 31, 2014
ACCUMULATED OTHER COMPEREHENSIVE LOSS
Schedule of changes in accumulated other comprehensive loss (AOCL) by components
		Cash flow
	(millions of dollars)	hedges
	Balance at December 31, 2011	(1	)
	Other comprehensive loss before reclassifications	–
	Amounts reclassified from AOCL (affected financial charges and other)	–
	Net other comprehensive loss	–
	Balance at December 31, 2012	(1	)
	Other comprehensive loss before reclassifications	–
	Amounts reclassified from AOCL (affected financial charges and other)	–
	Net other comprehensive loss	–
	Balance at December 31, 2013	(1	)
	Other comprehensive loss before reclassifications	(1	)
	Amounts reclassified from AOCL (affected financial charges and other)	–
	Net other comprehensive loss	(1	)
	Balance as of December 31, 2014	(2	)

FINANCIAL_CHARGES_AND_OTHER_Ta

FINANCIAL CHARGES AND OTHER (Tables)	12 Months Ended
	Dec. 31, 2014
FINANCIAL CHARGES AND OTHER
Schedule of financial charges and other
			2014		2013(a)	2012(a)
	Year ended December 31 (millions of dollars)
	Interest expense		48		42	40
	Amortization of debt issue costs		1		1	1
	Net realized loss related to the interest rate swaps and options		2		1	–
	Other		(1	)	–	(1	)
			50		44	40
	(a)	Recast as discussed in Note 2 and Note 6.

NET_INCOME_PER_COMMON_UNIT_Tab

NET INCOME PER COMMON UNIT (Tables)	12 Months Ended
	Dec. 31, 2014
NET INCOME PER COMMON UNIT
Schedule of net income per common unit
			2014	2013(a)		2012(a)
	(millions of dollars, except per common unit amounts)
	Net income attributable to controlling interests		172	155		192
	Net income attributed to GTN's and Bison's former parent(b)		–	(26	)	(55	)
	Net income allocated to controlling interests(b)		172	129		137
	Net income allocated to General Partner, including incentive distribution rights (IDRs)(c)		4	3		3
	Net income allocable to common units		168	126		134
	Weighted average common units outstanding (millions) – basic and diluted		62.7	58.9		53.5
	Net income per common unit – basic and diluted		$	$		$
			2.67	2.13		2.51
	(a)	Recast as discussed in Note 2 and Note 6.
	(b)	Net income allocated to controlling interests excludes net income attributed to GTN's and Bison's former parent as it was allocated to TransCanada and was not allocable to either the general partner or common units.
	(c)	In the calculation of basic and diluted net income per common unit, the net income allocated to the General Partner includes IDRs pertaining to the current reporting period, but declared and paid in the subsequent period.

CHANGE_IN_OPERATING_WORKING_CA1

CHANGE IN OPERATING WORKING CAPITAL (Tables)	12 Months Ended
	Dec. 31, 2014
CHANGE IN OPERATING WORKING CAPITAL
Summary of change in operating working capital
			2014	2013(a)		2012(a)
	Year Ended December 31 (millions of dollars)
	Change in accounts receivable and other		2	1		2
	Change in accounts payable and accrued liabilities		4	(9	)	(2	)
	Change in accounts payable to affiliates(b)		11	(2	)	–
	Change in accrued interest		–	2		–
	Change in operating working capital		17	(8	)	–
	(a)	Recast as discussed in Note 2 and Note 6.
	(b)	Excludes Carty Lateral accrual of $25 million at December 31, 2013.

TRANSACTIONS_WITH_MAJOR_CUSTOM1

TRANSACTIONS WITH MAJOR CUSTOMERS (Tables)	12 Months Ended
	Dec. 31, 2014
TRANSACTIONS WITH MAJOR CUSTOMERS
Schedule of revenues from major customers
			2014	2013(a)	2012(a)
	Year Ended December 31 (millions of dollars)
	Anadarko Energy Services Company (Anadarko)		48	48	48
	Pacific Gas and Electric Company (Pacific Gas)		45	46	47
	(a)	Recast as discussed in Note 2 and Note 6.

RELATED_PARTY_TRANSACTIONS_Tab

RELATED PARTY TRANSACTIONS (Tables)	12 Months Ended
	Dec. 31, 2014
RELATED PARTY TRANSACTIONS
Summary of capital and operating costs charged to pipeline systems by related party
			2014	2013	2012
	Year ended December 31 (millions of dollars)
	Capital and operating costs charged by TransCanada's subsidiaries to:
		GTN(a)(b)	30	28	29
		Northern Border(a)	35	30	31
		Bison(a)(b)(c)	6	5	6
		Great Lakes(a)	30	31	33
		North Baja	5	4	4
		Tuscarora	4	4	4
	Impact on the Partnership's net income attributable to controlling interests:
		GTN(b)	19	19	19
		Northern Border	16	14	14
		Bison(b)(c)	4	4	4
		Great Lakes	13	14	15
		North Baja	4	4	4
		Tuscarora	4	4	4
Summary of amount payable to related party for costs charged
			2014	2013
	December 31 (millions of dollars)
	Amount payable to TransCanada's subsidiaries for costs charged in the year by:
		GTN(a)	10	3
		Northern Border(a)	10	3
		Bison(a)	2	–
		Great Lakes(a)	9	3
		North Baja	1	1
		Tuscarora	1	–
	(a)	Represents 100 percent of the costs.
	(b)	Recast as discussed in Note 2 and Note 6.
	(c)	In 2014, the Partnership acquired remaining 30 percent interest in Bison. See discussion in Note 6.

QUARTERLY_FINANCIAL_DATA_unaud1

QUARTERLY FINANCIAL DATA (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
QUARTERLY FINANCIAL DATA (unaudited)
Schedule of selected unaudited financial data
			31-Mar	30-Jun	30-Sep	31-Dec
	Quarter ended (millions of dollars except per common unit amounts)
	2014
	Transmission revenues		87	82	80	87
	Equity earnings		33	18	15	22
	Net income		67	45	39	53
	Net income attributable to controlling interests		57	37	31	47
	Net income per common unit		$	$	$	$
			0.90	0.58	0.48	0.71
	Cash distribution paid		52	52	54	54
	2013
	Transmission revenues(a)		86	82	85	88
	Equity earnings(a)		18	15	15	19
	Net income(a)		53	42	46	50
	Net income attributable to controlling interests(a)		43	34	37	41
	Net income per common unit		$	$	$	$
			0.52	0.40	0.58	0.63
	Cash distributions paid		43	43	52	52
	(a)	Recast as discussed in Note 2 and Note 6.

FAIR_VALUE_MEASUREMENTS_Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2014
FAIR VALUE MEASUREMENTS
Schedule of estimated fair value of long-term debt
	2014		2013
		Carrying Value	Fair Value	Carrying Value	Fair Value
	December 31 (millions of dollars)
	Senior Credit Facility due 2017	330	330	380	380
	Term Loan Facility due 2018	500	500	500	500
	Short-Term Loan Facility due 2015	170	170	–	–
	4.65% Senior Notes due 2021	350	375	349	353
	5.09% Unsecured Senior Notes due 2015	75	76	75	79
	5.29% Unsecured Senior Notes due 2020	100	111	100	106
	5.69% Unsecured Senior Notes due 2035	150	168	150	154
	3.82% Series D Senior Notes due 2017	20	21	24	25
		1,695	1,751	1,578	1,597

ACCOUNTS_RECEIVABLE_AND_OTHER_

ACCOUNTS RECEIVABLE AND OTHER (Tables)	12 Months Ended
	Dec. 31, 2014
ACCOUNTS RECEIVABLE AND OTHER
Schedule of accounts receivable and other
		2014	2013
	December 31 (millions of dollars)
	Trade accounts receivable, net of allowance of nil	30	33
	Accounts receivable from affiliates	1	–
	Other	4	4
		35	37

ORGANIZATION_Details

ORGANIZATION (Details)	12 Months Ended
	Dec. 31, 2014	Mar. 31, 2014	Sep. 30, 2014
GTN
Organization
Ownership interest (as a percent)	70.00%
Northern Border
Organization
Ownership interest (as a percent)	50.00%
Bison
Organization
Ownership interest (as a percent)	100.00%
Great Lakes
Organization
Ownership interest (as a percent)	46.45%	46.45%
North Baja Pipeline, LLC
Organization
Ownership interest (as a percent)	100.00%
Tuscarora Gas Transmission Company
Organization
Ownership interest (as a percent)	100.00%
GTN
Organization
Length of pipeline owned (in miles)	1,353
Northern Border
Organization
Length of pipeline owned (in miles)	1,408
Bison
Organization
Length of pipeline owned (in miles)	303
Great Lakes
Organization
Length of pipeline owned (in miles)	2,115
North Baja Pipeline, LLC
Organization
Length of pipeline owned (in miles)	86
Tuscarora Gas Transmission Company
Organization
Length of pipeline owned (in miles)	305
TransCanada | GTN
Organization
Remaining noncontrolling ownership interest (as a percent)	30.00%
TransCanada | Bison
Organization
Remaining noncontrolling ownership interest (as a percent)			30.00%
TransCanada | Great Lakes
Organization
Remaining ownership interest (as a percent)	53.55%
ONEOK Partners, L.P. | Northern Border
Organization
Remaining ownership interest (as a percent)	50.00%

ORGANIZATION_Details_2

ORGANIZATION (Details 2)	0 Months Ended		12 Months Ended
	22-May-13	22-May-13	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Partners' Equity
Number of common units			63,600,000	62,300,000	53,500,000
Common Units (Limited Partners)
Partners' Equity
Number of common units			63,561,546	62,327,766	53,472,766
Limited partner interest (as a percent)			98.00%
TC PipeLines GP, Inc. | General Partner
Partners' Equity
Ownership interest in the Partnership (as a percent)	2.00%	2.00%	2.00%	2.00%	2.00%
TC PipeLines GP, Inc. | Common Units (Limited Partners)
Partners' Equity
Number of common units			5,797,106
TC PipeLines GP, Inc. | Common units and General Partner interest combined
Partners' Equity
Ownership interest in the Partnership (as a percent)			10.90%	11.10%	12.60%
TransCanada | Common Units (Limited Partners)
Partners' Equity
Number of common units			11,287,725
Limited partner interest (as a percent)			17.40%
TransCanada Corporation and subsidiaries | Common units and General Partner interest combined
Partners' Equity
Ownership interest in the Partnership (as a percent)			28.30%

SIGNIFICANT_ACCOUNTING_POLICIE2

SIGNIFICANT ACCOUNTING POLICIES (Details)	Sep. 30, 2014	Jul. 01, 2013	Oct. 01, 2014
Bison | TransCanada
Acquisition
Remaining noncontrolling ownership interest (as a percent)	30.00%
GTN | Former parent, TransCanada subsidiaries | Transaction between entities under common control
Acquisition
Interest acquired by Partnership (as a percent)		45.00%
Ownership interest, including acquired interest (as a percent)		70.00%
Bison | Former parent, TransCanada subsidiaries | Transaction between entities under common control
Acquisition
Interest acquired by Partnership (as a percent)		45.00%	30.00%
Ownership interest, including acquired interest (as a percent)		70.00%

SIGNIFICANT_ACCOUNTING_POLICIE3

SIGNIFICANT ACCOUNTING POLICIES (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Pipeline facilities and compression equipment | Minimum
PLANT, PROPERTY AND EQUIPMENT
Estimated useful lives	20 years
Pipeline facilities and compression equipment | Maximum
PLANT, PROPERTY AND EQUIPMENT
Estimated useful lives	77 years
Metering and other | Minimum
PLANT, PROPERTY AND EQUIPMENT
Estimated useful lives	5 years
Metering and other | Maximum
PLANT, PROPERTY AND EQUIPMENT
Estimated useful lives	77 years
Pipeline
Asset Retirement Obligation
Asset retirement liabilities	0	$0

INVESTMENTS_IN_UNCONSOLIDATED_2

INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Details) (USD $)	3 Months Ended								12 Months Ended					1 Months Ended	0 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012		Apr. 30, 2006	Jan. 01, 2013	Nov. 14, 2013	Feb. 28, 2007
Investments in unconsolidated affiliates
Equity Earnings (Loss) from Unconsolidated Affiliates	$22	$15	$18	$33	$19	$15	$15	$18	$88	$67	[1]	$99	[1]
Investments in Unconsolidated Affiliates	1,177				1,195				1,177	1,195
Northern Border
Investments in unconsolidated affiliates
Transaction fee														10
Interest acquired (as a percent)														20.00%
Great Lakes
Investments in unconsolidated affiliates
Interest acquired (as a percent)																	46.45%
Northern Border
Investments in unconsolidated affiliates
Term of moratorium on filing rate cases															3 years
Great Lakes
Investments in unconsolidated affiliates
Increase in transportation rates compared to current rates (as a percent)																21.00%
Total cash call issued to fund debt repayment	10			9
Northern Border
Investments in unconsolidated affiliates
Ownership interest (as a percent)	50.00%								50.00%
Equity Earnings (Loss) from Unconsolidated Affiliates									69	64		72
Investments in Unconsolidated Affiliates	505				523				505	523
Amortization period of transaction fee														12 years
Undistributed earnings									0	0		0
Amount of difference between the carrying value and the underlying equity in net assets resulting from the recognition and inclusion of goodwill	117				118				117	118
Equity contribution										31	[1]
Assets
Cash and cash equivalents	41				27				41	27
Other current assets	34				34				34	34
Plant, property and equipment, net	1,163				1,197				1,163	1,197
Other assets	34				33				34	33
Assets, total	1,272				1,291				1,272	1,291
LIABILITIES AND PARTNERS' EQUITY
Current liabilities	64				51				64	51
Deferred credits and other	22				19				22	19
Long-term debt	411				411				411	411
Partners' equity
Partners' equity	777				812				777	812
Accumulated other comprehensive loss	-2				-2				-2	-2
Liabilities and Equity, total	1,272				1,291				1,272	1,291
Revenues (expenses)
Transmission revenues									293	286		311
Operating expenses									-72	-75		-79
Depreciation									-59	-58		-63
Financial charges and other									-22	-23		-24
Net income									140	130		145
Northern Border | ONEOK Partners, L.P.
Investments in unconsolidated affiliates
Other ownership interest (as a percent)	50.00%								50.00%
TC PipeLines Intermediate Limited Partnership
Investments in unconsolidated affiliates
Partnership interest held (as a percent)									98.99%
Great Lakes
Investments in unconsolidated affiliates
Ownership interest (as a percent)	46.45%			46.45%					46.45%
Equity Earnings (Loss) from Unconsolidated Affiliates									19	3		27
Investments in Unconsolidated Affiliates	672				672				672	672
Undistributed earnings									0	0		0
Amount of difference between the carrying value and the underlying equity in net assets resulting from the recognition and inclusion of goodwill	458				458				458	458
Equity contribution	5			4					9	9	[1]	9	[1]
Assets
Current assets	66				52				66	52
Plant, property and equipment, net	748				771				748	771
Assets, total	814				823				814	823
LIABILITIES AND PARTNERS' EQUITY
Current liabilities	38				28				38	28
Long-term debt, including current maturities	316				335				316	335
Partners' equity
Partners' equity	460				460				460	460
Liabilities and Equity, total	814				823				814	823
Revenues (expenses)
Transmission revenues									146	124		182
Operating expenses									-53	-60		-66
Depreciation									-28	-31		-31
Financial charges and other									-25	-27		-28
Net income									$40	$6		$57
Great Lakes | TransCanada
Investments in unconsolidated affiliates
Other ownership interest (as a percent)	53.55%								53.55%
TC GL Intermediate Limited Partnership
Investments in unconsolidated affiliates
Partnership interest held (as a percent)									98.99%
[1]	Recast as discussed in Note 2 and Note 6.

PLANT_PROPERTY_AND_EQUIPMENT_D

PLANT, PROPERTY AND EQUIPMENT (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
PLANT, PROPERTY AND EQUIPMENT
Cost	$2,705	$2,716
Accumulated Depreciation	-737	-674
Net Book Value	1,968	2,042
Pipeline
PLANT, PROPERTY AND EQUIPMENT
Cost	2,038	2,045
Accumulated Depreciation	-574	-522
Net Book Value	1,464	1,523
Compression
PLANT, PROPERTY AND EQUIPMENT
Cost	514	520
Accumulated Depreciation	-126	-120
Net Book Value	388	400
Metering and other
PLANT, PROPERTY AND EQUIPMENT
Cost	145	146
Accumulated Depreciation	-37	-32
Net Book Value	108	114
Construction in progress
PLANT, PROPERTY AND EQUIPMENT
Cost	8	5
Net Book Value	$8	$5

ACQUISITIONS_Details

ACQUISITIONS (Details) (USD $)	12 Months Ended	0 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Oct. 01, 2014	Jul. 01, 2013	Sep. 30, 2014
Bison
Acquisition
Total cash consideration	$217
TransCanada's carrying value of non-controlling interest at October 1, 2014 / Excess purchase price	217
Bison | Common Units (Limited Partners)
Acquisition
TransCanada's carrying value of non-controlling interest at October 1, 2014 / Excess purchase price	29
Bison | Non-controlling interests
Acquisition
TransCanada's carrying value of non-controlling interest at October 1, 2014 / Excess purchase price	188
Bison | Former parent, TransCanada subsidiaries | Transaction between entities under common control
Acquisition
Interest acquired by Partnership (as a percent)		30.00%	45.00%
Purchase price		215	300
Purchase price adjustments		2
Total cash consideration		217
Bison | Former parent, TransCanada subsidiaries | Common Units (Limited Partners) | Transaction between entities under common control
Acquisition
TransCanada's carrying value of non-controlling interest at October 1, 2014 / Excess purchase price		29
Bison | Former parent, TransCanada subsidiaries | Non-controlling interests | Transaction between entities under common control
Acquisition
TransCanada's carrying value of non-controlling interest at October 1, 2014 / Excess purchase price		$188
TransCanada | Bison
Acquisition
Remaining noncontrolling ownership interest (as a percent)				30.00%

ACQUISITIONS_Details_Details_2

ACQUISITIONS (Details Details 2) (USD $)	0 Months Ended			12 Months Ended				0 Months Ended
In Millions, except Share data, unless otherwise specified	22-May-13	Jul. 02, 2013	22-May-13	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012	Jul. 01, 2013	Apr. 11, 2013	Oct. 01, 2014	Jun. 30, 2013
Equity Issuance, May 2013 | Common Units (Limited Partners)
Acquisition
Units sold in public offering	8,855,000
Price per common unit in public offering	$43.85		43.85
Net proceeds from issuance of common units	$373
Term Loan Facility due 2018
Acquisition
Borrowings under the facility		500
Maximum borrowing capacity								500
Senior Credit Facility due 2017 | Senior revolving credit facility
Acquisition
Maximum borrowing capacity								500
TC PipeLines GP, Inc. | Equity Issuance, May 2013 | General Partner
Acquisition
Capital contribution	8
TC PipeLines GP, Inc. | General Partner
Acquisition
Ownership interest in the Partnership (as a percent)	2.00%		2.00%	2.00%	2.00%		2.00%
GTN and Bison
Acquisition
Cash paid					921	[1]
GTN and Bison | Former parent, TransCanada subsidiaries | Transaction between entities under common control
Acquisition
Purchase price								1,050
Working capital adjustments								17
Cash paid								921
Recorded purchase price
Current assets								67
Property, plant and equipment, net								1,792
Other assets								1
Current liabilities								-20
Other liabilities								-21
Long-term debt								-325
Net assets acquired								1,494
Carrying value of acquired 45% interest in each of GTN and Bison								672
Excess purchase price over net assets acquired (includes Carty Lateral consideration)								274
Total cash consideration including $25 million Carty Lateral consideration								946
Increase in the net income attributable to common units resulting from retrospective consolidation					26		55
GTN and Bison | Former parent, TransCanada subsidiaries | Transaction between entities under common control | Carrying value
Recorded purchase price
Non-controlling interest								-448
Carrying value of pre-existing 25% interest in each of GTN and Bison								-374
GTN
Acquisition
Payment with respect to the Carty Lateral consideration				25
GTN | Former parent, TransCanada subsidiaries | Transaction between entities under common control
Acquisition
Interest acquired by Partnership (as a percent)								45.00%
Ownership interest, including acquired interest (as a percent)								70.00%
Purchase price								750
Acquired debt								146
Contingent additional payment, maximum								25
Payment with respect to the Carty Lateral consideration									25
Recorded purchase price
Excess purchase price over net assets acquired (includes Carty Lateral consideration)								262
Pre-existing interest acquired by the partnership (as a percent)											25.00%
GTN | Former parent, TransCanada subsidiaries | Transaction between entities under common control | Accounts payable to affiliates
Recorded purchase price
Contingent consideration					25
Bison | Former parent, TransCanada subsidiaries | Transaction between entities under common control
Acquisition
Interest acquired by Partnership (as a percent)								45.00%		30.00%
Ownership interest, including acquired interest (as a percent)								70.00%
Purchase price								300		215
Working capital adjustments										2
Recorded purchase price
Excess purchase price over net assets acquired (includes Carty Lateral consideration)								$12
Pre-existing interest acquired by the partnership (as a percent)											25.00%
[1]	Recast as discussed in Note 2 and Note 6.

CREDIT_FACILITIES_SHORTTERM_LO2

CREDIT FACILITIES, SHORT-TERM LOAN FACILITY AND LONG-TERM DEBT (Details) (USD $)	12 Months Ended	0 Months Ended	3 Months Ended	12 Months Ended		0 Months Ended
	Dec. 31, 2014	Oct. 01, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jul. 02, 2013	Jul. 01, 2013	Dec. 31, 2014
Credit facilities, short-term loan facility and long-term debt
Credit facilities, short-term loan facility and long-term debt	$1,695,000,000		1,695,000,000	1,578,000,000				1,695,000,000
Less: current portion	249,000,000		249,000,000	3,000,000				249,000,000
Long-term debt	1,446,000,000		1,446,000,000	1,575,000,000				1,446,000,000
Borrowings under facility	170,000,000
Term loan
Credit facilities, short-term loan facility and long-term debt
Credit facilities, short-term loan facility and long-term debt	170,000,000		170,000,000					170,000,000
Amount of facility		170,000,000
Borrowings under facility		170,000,000
Term of the facility		364 days
Term loan | LIBOR
Credit facilities, short-term loan facility and long-term debt
Variable rate basis		one-month LIBOR
Basis spread on variable rate (as a percent)		1.00%
Debt average interest rate (as a percent)			1.28%
Debt interest rate, at period end (as a percent)	1.28%		1.28%					1.28%
Term loan | Prime rate
Credit facilities, short-term loan facility and long-term debt
Variable rate basis		prime rate
Term loan | Federal funds rate
Credit facilities, short-term loan facility and long-term debt
Variable rate basis		federal funds rate
Basis spread on variable rate (as a percent)		0.50%
Senior Credit Facility due 2017
Credit facilities, short-term loan facility and long-term debt
Credit facilities, short-term loan facility and long-term debt	330,000,000		330,000,000	380,000,000				330,000,000
Senior Credit Facility due 2017 | Maximum
Credit facilities, short-term loan facility and long-term debt
Option to increase credit facility borrowing capacity	250,000,000		250,000,000					250,000,000
Senior Credit Facility due 2017 | LIBOR
Credit facilities, short-term loan facility and long-term debt
Variable rate basis	LIBOR			LIBOR	LIBOR
Debt average interest rate (as a percent)	1.41%			1.44%	1.61%
Debt interest rate, at period end (as a percent)	1.41%		1.41%	1.42%				1.41%
Senior Credit Facility due 2017 | Senior revolving credit facility
Credit facilities, short-term loan facility and long-term debt
Maximum borrowing capacity	500,000,000		500,000,000					500,000,000
Amount outstanding under credit facility	330,000,000		330,000,000	380,000,000				330,000,000
Remaining borrowing capacity	170,000,000		170,000,000					170,000,000
Term Loan Facility due 2018
Credit facilities, short-term loan facility and long-term debt
Credit facilities, short-term loan facility and long-term debt	500,000,000		500,000,000	500,000,000				500,000,000
Maximum borrowing capacity							500,000,000
Borrowings under the facility						500,000,000
Term Loan Facility due 2018 | LIBOR borrowings | LIBOR
Credit facilities, short-term loan facility and long-term debt
Variable rate basis	LIBOR			LIBOR			LIBOR
Debt average interest rate (as a percent)	1.41%			1.43%
Debt interest rate, at period end (as a percent)	1.41%		1.41%	1.42%				1.41%
Term Loan Facility due 2018 | LIBOR borrowings | LIBOR | Minimum
Credit facilities, short-term loan facility and long-term debt
Basis spread on variable rate (as a percent)							1.13%
Term Loan Facility due 2018 | LIBOR borrowings | LIBOR | Maximum
Credit facilities, short-term loan facility and long-term debt
Basis spread on variable rate (as a percent)							2.00%
Term Loan Facility due 2018 | LIBOR borrowings | LIBOR | Hedges of cash flows | Interest rate swaps
Credit facilities, short-term loan facility and long-term debt
Debt average interest rate (as a percent)	1.82%			1.70%
Term Loan Facility due 2018 | Base rate borrowings | LIBOR
Credit facilities, short-term loan facility and long-term debt
Variable rate basis							one-month LIBOR
Basis spread on variable rate (as a percent)							1.00%
Term Loan Facility due 2018 | Base rate borrowings | Base rate
Credit facilities, short-term loan facility and long-term debt
Variable rate basis							Lender prime rate, federal funds rate or one-month LIBOR
Term Loan Facility due 2018 | Base rate borrowings | Base rate | Minimum
Credit facilities, short-term loan facility and long-term debt
Basis spread on variable rate (as a percent)							0.13%
Term Loan Facility due 2018 | Base rate borrowings | Base rate | Maximum
Credit facilities, short-term loan facility and long-term debt
Basis spread on variable rate (as a percent)							1.00%
Term Loan Facility due 2018 | Base rate borrowings | Prime rate
Credit facilities, short-term loan facility and long-term debt
Variable rate basis							prime rate
Term Loan Facility due 2018 | Base rate borrowings | Federal funds rate
Credit facilities, short-term loan facility and long-term debt
Variable rate basis							federal funds rate
Basis spread on variable rate (as a percent)							0.50%
Senior Credit Facility, Term Loan Facilities and Short-Term Loan Facility
Credit facilities, short-term loan facility and long-term debt
Leverage ratio (as a percent)								436.00%
Senior Credit Facility, Term Loan Facilities and Short-Term Loan Facility | Debt agreement covenants, period prior to occurrence of specified material acquisition | Maximum
Credit facilities, short-term loan facility and long-term debt
Leverage ratio (as a percent)	500.00%
Senior Credit Facility, Term Loan Facilities and Short-Term Loan Facility | Debt agreement covenants, initial period after occurrence of specified material 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, Term Loan Facilities and Short-Term Loan Facility | Debt agreement covenants, initial period after occurrence of specified material acquisition | Maximum
Credit facilities, short-term loan facility and long-term debt
Leverage ratio (as a percent)	550.00%
Senior Credit Facility, Term Loan Facilities and Short-Term Loan Facility | Debt agreement covenants, periods subsequent to initial period after occurrence of specified material acquisition | Maximum
Credit facilities, short-term loan facility and long-term debt
Leverage ratio (as a percent)	500.00%
4.65% Senior Notes due 2021
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	4.65%		4.65%	4.65%				4.65%
Credit facilities, short-term loan facility and long-term debt	350,000,000		350,000,000	349,000,000				350,000,000
5.09% Unsecured Senior Notes due 2015
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	5.09%		5.09%	5.09%				5.09%
Credit facilities, short-term loan facility and long-term debt	75,000,000		75,000,000	75,000,000				75,000,000
5.29% Unsecured Senior Notes due 2020
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	5.29%		5.29%	5.29%				5.29%
Credit facilities, short-term loan facility and long-term debt	100,000,000		100,000,000	100,000,000				100,000,000
5.69% Unsecured Senior Notes due 2035
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	5.69%		5.69%	5.69%				5.69%
Credit facilities, short-term loan facility and long-term debt	150,000,000		150,000,000	150,000,000				150,000,000
3.82% Series D Senior Notes due 2017
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	3.82%		3.82%	3.82%				3.82%
Credit facilities, short-term loan facility and long-term debt	$20,000,000		20,000,000	24,000,000				20,000,000
GTN | 5.09% Unsecured Senior Notes due 2015
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	5.09%		5.09%					5.09%
GTN | Senior Notes | Maximum
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization	70.00%

CREDIT_FACILITIES_SHORTTERM_LO3

CREDIT FACILITIES, SHORT-TERM LOAN FACILITY AND LONG-TERM DEBT (Details 2) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Principal repayments required by the Partnership on the long-term debt
2015	$249	$3
2016	4
2017	342
2018	500
Thereafter	600
Total credit facilities and long-term debt	$1,695	$1,578

OTHER_LIABILITIES_Details

OTHER LIABILITIES (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
OTHER LIABILITIES
Regulatory liabilities	$23	$22
Other liabilities	3	2
Other liabilities, total	$26	$24

PARTNERS_EQUITY_Details

PARTNERS' EQUITY (Details) (USD $)	12 Months Ended	0 Months Ended		12 Months Ended		1 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	22-May-13	22-May-13	Dec. 31, 2013	Dec. 31, 2012	Aug. 31, 2014
						Institution
Partners' Equity
Number of common units	63,600,000			62,300,000	53,500,000
Common Units (Limited Partners)
Partners' Equity
Number of common units	63,561,546			62,327,766	53,472,766
Ownership interest in the Partnership (as a percent)	98.00%
TC PipeLines GP, Inc. | Common Units (Limited Partners)
Partners' Equity
Number of common units	5,797,106
TC PipeLines GP, Inc. | General Partner
Partners' Equity
Ownership interest in the Partnership (as a percent)	2.00%	2.00%	2.00%	2.00%	2.00%
TC PipeLines GP, Inc. | Common units and General Partner interest combined
Partners' Equity
Ownership interest in the Partnership (as a percent)	10.90%			11.10%	12.60%
TransCanada | Common Units (Limited Partners)
Partners' Equity
Number of common units	11,287,725
Ownership interest in the Partnership (as a percent)	17.40%
ATM Equity Issuance Program | Common Units (Limited Partners)
Partners' Equity
Number of financial institutions						5
Units sold	1,300,000
Sales agent commissions	1
Net proceeds from public offering of common units	72
ATM Equity Issuance Program | TC PipeLines GP, Inc. | General Partner
Partners' Equity
Equity contribution	1
ATM Equity Issuance Program | Maximum | Expected | Common Units (Limited Partners)
Partners' Equity
Gross proceeds from sale of common units						200
ATM Equity Issuance Program | Minimum | Common Units (Limited Partners)
Partners' Equity
Number of managers to agree with equity sale method						1
Equity Issuance, May 2013 | Common Units (Limited Partners)
Partners' Equity
Units sold		8,855,000
Units sold in public offering pursuant to exercise of underwriters' option		1,155,000
Price per common unit in public offering		43.85	43.85
Gross proceeds from sale of common units		388
Net proceeds from public offering of common units		373
Equity Issuance, May 2013 | TC PipeLines GP, Inc. | General Partner
Partners' Equity
Equity contribution		8

ACCUMULATED_OTHER_COMPEREHENSI2

ACCUMULATED OTHER COMPEREHENSIVE LOSS (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Changes in accumulated other comprehensive loss (AOCL) by components
AOCL Balance as of beginning year		($1)
AOCL Balance as of end year	-2	-1
Cash flow hedges
Changes in accumulated other comprehensive loss (AOCL) by components
AOCL Balance as of beginning year	-1		-1	-1
Other comprehensive loss before reclassifications	-1
Net other comprehensive income (loss)	-1
AOCL Balance as of end year	($2)		($1)	($1)

FINANCIAL_CHARGES_AND_OTHER_De

FINANCIAL CHARGES AND OTHER (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
FINANCIAL CHARGES AND OTHER
Interest expense	$48	$42		$40
Amortization of debt issue costs (Note 11)	1	1	[1]	1	[1]
Net realized loss related to the interest rate swaps and options	2	1
Other	-1			-1
Financial charges and other	($50)	($44)	[1]	($40)	[1]
[1]	Recast as discussed in Note 2 and Note 6.

NET_INCOME_PER_COMMON_UNIT_Det

NET INCOME PER COMMON UNIT (Details) (USD $)	0 Months Ended		12 Months Ended
In Millions, unless otherwise specified	22-May-13	22-May-13	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
General Partner
Partners' Equity
Incentive distributions allocated to General Partner			1	0	0
TC PipeLines GP, Inc. | General Partner
Partners' Equity
General partner interest (as a percent)	2.00%	2.00%	2.00%	2.00%	2.00%

NET_INCOME_PER_COMMON_UNIT_Det1

NET INCOME PER COMMON UNIT (Details 2) (USD $)	3 Months Ended								12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Net income per common unit
Net income attributable to controlling interests	$47	$31	$37	$57	$41	$37	$34	$43	$172	$155	[1]	$192	[1]
Net income allocated to controlling interests									172	129	[1]	137	[1]
Net income allocated to General Partner, including incentive distribution rights (IDRs)									4	3	[1]	3	[1]
Net income allocable to common units									168	126	[1]	134	[1]
Weighted average common units outstanding (millions) - basic (in units)									62.7	58.9		53.5
Weighted average common units outstanding (millions) - diluted (in units)									62.7	58.9		53.5
Net income per common unit - basic (in dollars per unit)	$0.71	$0.48	$0.58	$0.90	$0.63	$0.58	$0.40	$0.52	$2.67	$2.13		$2.51
Net income per common unit - diluted (in dollars per unit)									$2.67	$2.13		$2.51
Former parent, TransCanada subsidiaries | Equity of former parent | GTN and Bison
Net income per common unit
Net income attributed to GTN and Bison's former parent										($26)	[1]	($55)	[1]
[1]	Recast as discussed in Note 2 and Note 6.

CASH_DISTRIBUTIONS_Details

CASH DISTRIBUTIONS (Details) (USD $)	3 Months Ended				12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2014
CASH DISTRIBUTIONS
Period after the end of each quarter within which quarterly cash distributions to partners are to be paid					45 days
Quarterly distribution (in dollars per unit)	$0.84	$0.84	$0.84	$0.81

CASH_DISTRIBUTIONS_Details_2

CASH DISTRIBUTIONS (Details 2) (General Partner, USD $)	12 Months Ended
	Dec. 31, 2014
Target level of $0.81 per common unit | Minimum
Incentive distributions
Combined general partner interest and incentive distribution interest percentage of quarterly distributions of Available Cash exceeding target levels, threshold	15.00%
Target level of quarterly distributions (in dollars per common unit)	$0.81
Target level of $0.88 per common unit | Minimum
Incentive distributions
Target level of quarterly distributions (in dollars per common unit)	$0.88
Target level of $0.88 per common unit | Maximum
Incentive distributions
Combined general partner interest and incentive distribution interest percentage of quarterly distributions of Available Cash exceeding target levels, threshold	25.00%

CASH_DISTRIBUTIONS_Details_3

CASH DISTRIBUTIONS (Details 3) (USD $)	3 Months Ended								12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Partnership distribution (in dollars per unit)									$3.30	$3.18	$3.10
Partnership distribution	$54	$54	$52	$52	$52	$52	$43	$43
General Partner
Incentive distributions									1	0	0
Percentage of priority income allocations for incentive distributions									100.00%
Common units and General Partner interest combined
Partnership distribution									212
Common Units (Limited Partners)
Partnership distribution										$188	$169

CHANGE_IN_OPERATING_WORKING_CA2

CHANGE IN OPERATING WORKING CAPITAL (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
CHANGE IN OPERATING WORKING CAPITAL
Change in accounts receivable and other	$2	$1		$2
Change in accounts payable and accrued liabilities	4	-9		-2
Change in accounts payable to affiliates(b)	11	-2
Change in accrued interest		2
Change in operating working capital	$17	($8)	[1]
[1]	Recast as discussed in Note 2 and Note 6.

CHANGE_IN_OPERATING_WORKING_CA3

CHANGE IN OPERATING WORKING CAPITAL (Details 2) (GTN, Former parent, TransCanada subsidiaries, Transaction between entities under common control, Accounts payable to affiliates, USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
GTN | Former parent, TransCanada subsidiaries | Transaction between entities under common control | Accounts payable to affiliates
Acquisition
Accrued additional consideration for Carty Lateral	$25

TRANSACTIONS_WITH_MAJOR_CUSTOM2

TRANSACTIONS WITH MAJOR CUSTOMERS (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Transactions with major customers
Revenues	$87	$80	$82	$87	$88	$85	$82	$86	$336	$341	[1]	$343	[1]
Accounts receivable and other	35				37				35	37
Total revenues | Major customers | Anadarko Energy Services Company
Transactions with major customers
Revenues									48	48		48
Total revenues | Major customers | Pacific Gas and Electric Company
Transactions with major customers
Revenues									45	46		47
Accounts receivable and other | Amounts owed by major customers | Anadarko Energy Services Company
Transactions with major customers
Accounts receivable and other	4				4				4	4
Accounts receivable and other | Amounts owed by major customers | Pacific Gas and Electric Company
Transactions with major customers
Accounts receivable and other	$4				$4				$4	$4
[1]	Recast as discussed in Note 2 and Note 6.

RELATED_PARTY_TRANSACTIONS_Det

RELATED PARTY TRANSACTIONS (Details) (USD $)	3 Months Ended			12 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 01, 2014	Jul. 01, 2013
Related party transactions
Accounts payable to affiliates		$15		$15	$29
Amount included in receivables from related party		1		1
Bison
Related party transactions
Total cash call issued to fund debt repayment	24
Bison | Former parent, TransCanada subsidiaries
Related party transactions
Capital contribution	18
Great Lakes
Related party transactions
Total cash call issued to fund debt repayment		10	9
Bison | Former parent, TransCanada subsidiaries
Related party transactions
Ownership interest (as a percent)	75.00%
General Partner | Reimbursement of costs of services provided
Related party transactions
Costs charged				3	3	3
TransCanada's subsidiaries | GTN
Related party transactions
Accounts payable to affiliates		10		10	3
TransCanada's subsidiaries | GTN | Capital and operating costs
Related party transactions
Costs charged				30	28	29
Impact on the Partnership's net income attributable to controlling interests				19	19	19
Percentage of capital and operating costs charged				100.00%	100.00%	100.00%
TransCanada's subsidiaries | Northern Border
Related party transactions
Accounts payable to affiliates		10		10	3
TransCanada's subsidiaries | Northern Border | Capital and operating costs
Related party transactions
Costs charged				35	30	31
Impact on the Partnership's net income attributable to controlling interests				16	14	14
Percentage of capital and operating costs charged				100.00%	100.00%	100.00%
TransCanada's subsidiaries | Bison
Related party transactions
Accounts payable to affiliates		2		2
TransCanada's subsidiaries | Bison | Capital and operating costs
Related party transactions
Costs charged				6	5	6
Impact on the Partnership's net income attributable to controlling interests				4	4	4
Percentage of capital and operating costs charged				100.00%	100.00%	100.00%
TransCanada's subsidiaries | Great Lakes
Related party transactions
Accounts payable to affiliates		9		9	3
Amount included in receivables from related party		15		15	11
TransCanada's subsidiaries | Great Lakes | Capital and operating costs
Related party transactions
Costs charged				30	31	33
Impact on the Partnership's net income attributable to controlling interests				13	14	15
Percentage of capital and operating costs charged				100.00%	100.00%	100.00%
TransCanada's subsidiaries | Great Lakes | Transportation contracts
Related party transactions
Revenues from related party				71	68	77
TransCanada's subsidiaries | Great Lakes | Transportation contracts | Total revenues | Major customers
Related party transactions
Percent of total revenues				49.00%	55.00%	42.00%
TransCanada's subsidiaries | Great Lakes | Affiliated rental revenue
Related party transactions
Revenues from related party				2	1	1
TransCanada's subsidiaries | North Baja Pipeline, LLC
Related party transactions
Accounts payable to affiliates		1		1	1
TransCanada's subsidiaries | North Baja Pipeline, LLC | Capital and operating costs
Related party transactions
Costs charged				5	4	4
Impact on the Partnership's net income attributable to controlling interests				4	4	4
TransCanada's subsidiaries | Tuscarora Gas Transmission Company
Related party transactions
Accounts payable to affiliates		1		1
TransCanada's subsidiaries | Tuscarora Gas Transmission Company | Capital and operating costs
Related party transactions
Costs charged				4	4	4
Impact on the Partnership's net income attributable to controlling interests				4	4	4
TransCanada's subsidiaries | Great Lakes
Related party transactions
Revenue from TransCanada and its affiliates included in the Partnership's equity earnings				34	32	36
ANR Pipeline Company | Great Lakes | Seasonal firm service between Michigan and Wisconsin
Related party transactions
Deferred revenue		9.4		9.4
Bison | Former parent, TransCanada subsidiaries | Transaction between entities under common control
Related party transactions
Interest acquired by Partnership (as a percent)							30.00%	45.00%
GTN | Former parent, TransCanada subsidiaries | Transaction between entities under common control
Related party transactions
Interest acquired by Partnership (as a percent)								45.00%
GTN | Former parent, TransCanada subsidiaries | Transaction between entities under common control | Accounts payable to affiliates
Related party transactions
Accrued additional consideration					$25

QUARTERLY_FINANCIAL_DATA_unaud2

QUARTERLY FINANCIAL DATA (unaudited) (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Quarterly financial data (unaudited)
Transmission revenues	$87	$80	$82	$87	$88	$85	$82	$86	$336	$341	[1]	$343	[1]
Equity earnings	22	15	18	33	19	15	15	18	88	67	[1]	99	[1]
Net income	53	39	45	67	50	46	42	53	204	191	[1]	229	[1]
Net income attributable to controlling interests	47	31	37	57	41	37	34	43	172	155	[1]	192	[1]
Net income per common unit (in dollars per unit)	$0.71	$0.48	$0.58	$0.90	$0.63	$0.58	$0.40	$0.52	$2.67	$2.13		$2.51
Cash distributions paid	$54	$54	$52	$52	$52	$52	$43	$43
[1]	Recast as discussed in Note 2 and Note 6.

FAIR_VALUE_MEASUREMENTS_Detail

FAIR VALUE MEASUREMENTS (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
4.65% Senior Notes due 2021
Financial Instruments
Stated interest rate (as a percent)	4.65%	4.65%
5.09% Unsecured Senior Notes due 2015
Financial Instruments
Stated interest rate (as a percent)	5.09%	5.09%
5.29% Unsecured Senior Notes due 2020
Financial Instruments
Stated interest rate (as a percent)	5.29%	5.29%
5.69% Unsecured Senior Notes due 2035
Financial Instruments
Stated interest rate (as a percent)	5.69%	5.69%
3.82% Series D Senior Notes due 2017
Financial Instruments
Stated interest rate (as a percent)	3.82%	3.82%
Carrying Value.
Financial Instruments
Debt	1,695	1,578
Carrying Value. | Senior Credit Facility due 2017 | Senior revolving credit facility
Financial Instruments
Debt	330	380
Carrying Value. | Term Loan Facility due 2018
Financial Instruments
Debt	500	500
Carrying Value. | Short-Term Loan due 2015 | Term loan
Financial Instruments
Debt	170
Carrying Value. | 4.65% Senior Notes due 2021
Financial Instruments
Debt	350	349
Carrying Value. | 5.09% Unsecured Senior Notes due 2015
Financial Instruments
Debt	75	75
Carrying Value. | 5.29% Unsecured Senior Notes due 2020
Financial Instruments
Debt	100	100
Carrying Value. | 5.69% Unsecured Senior Notes due 2035
Financial Instruments
Debt	150	150
Carrying Value. | 3.82% Series D Senior Notes due 2017
Financial Instruments
Debt	20	24
Fair Value | Level 2
Financial Instruments
Debt	1,751	1,597
Fair Value | Level 2 | Senior Credit Facility due 2017 | Senior revolving credit facility
Financial Instruments
Debt	330	380
Fair Value | Level 2 | Term Loan Facility due 2018
Financial Instruments
Debt	500	500
Fair Value | Level 2 | Short-Term Loan due 2015 | Term loan
Financial Instruments
Debt	170
Fair Value | Level 2 | 4.65% Senior Notes due 2021
Financial Instruments
Debt	375	353
Fair Value | Level 2 | 5.09% Unsecured Senior Notes due 2015
Financial Instruments
Debt	76	79
Fair Value | Level 2 | 5.29% Unsecured Senior Notes due 2020
Financial Instruments
Debt	111	106
Fair Value | Level 2 | 5.69% Unsecured Senior Notes due 2035
Financial Instruments
Debt	168	154
Fair Value | Level 2 | 3.82% Series D Senior Notes due 2017
Financial Instruments
Debt	21	25

FAIR_VALUE_MEASUREMENTS_Detail1

FAIR VALUE MEASUREMENTS (Details 2) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts receivable
Interest rate derivatives
Maximum counterparty credit exposure related to accounts receivable	$35	$37
Interest rate swaps from September 3, 2013 through July 1, 2018 | Term Loan Facility due 2018
Interest rate derivatives
Amount of variable-rate debt hedged	150
Date of maturity	1-Jul-18
Weighted average fixed interest rate (as a percent)	2.79%
Hedges of cash flows | Interest rate swaps
Interest rate derivatives
Change in fair value of interest rate derivative instruments recognized in other comprehensive income		1
Hedges of cash flows | Interest rate swaps | Maximum
Interest rate derivatives
Change in fair value of interest rate derivative instruments recognized in other comprehensive income	1	1	0
Hedges of cash flows | Interest rate swaps | Financial charges and other
Interest rate derivatives
Net realized loss related to the interest rate swaps	2	1	0
Designated as hedge | Interest rate swaps | Recurring fair value measurement | Level 2
Interest rate derivatives
Fair value of derivatives, gross	1		0
Fair value of derivatives, net	1		0
Designated as hedge | Interest rate swaps | Recurring fair value measurement | Level 2 | Maximum
Interest rate derivatives
Fair value of derivatives, gross		1
Fair value of derivatives, net		$1

ACCOUNTS_RECEIVABLE_AND_OTHER_1

ACCOUNTS RECEIVABLE AND OTHER (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
ACCOUNTS RECEIVABLE AND OTHER
Trade accounts receivable, net of allowance of nil	$30	$33
Accounts receivable from affiliates	1
Other	4	4
Accounts receivable and other	$35	$37

CONTINGENCIES_Details

CONTINGENCIES (Details) (GTN, PaciCorp suit against GTN and Northwest Pipeline for alleged equipment damage, USD $)	1 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2009
GTN | PaciCorp suit against GTN and Northwest Pipeline for alleged equipment damage
Contingencies
Loss contingency, alleged damage amount	$7

SUBSEQUENT_EVENTS_Details

SUBSEQUENT EVENTS (Details) (USD $)

3 Months Ended

12 Months Ended

0 Months Ended

In Millions, except Share data, unless otherwise specified

Dec. 31, 2014

Sep. 30, 2014

Jun. 30, 2014

Mar. 31, 2014

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

22-May-13

22-May-13

Jan. 22, 2015

Feb. 02, 2015

Jan. 08, 2015

Feb. 13, 2015

Jan. 12, 2015

Distributions

Cash distribution (in dollars per unit)

$0.84

$0.84

$0.84

$0.81

Partnership distribution

$54

$54

$52

$52

$52

$52

$43

$43

Number of common units

63,600,000

62,300,000

63,600,000

62,300,000

53,500,000

GTN

Distributions

Partnership interest held (as a percent)

70.00%

Northern Border

Distributions

Ownership interest (as a percent)

50.00%

50.00%

Great Lakes

Distributions

Ownership interest (as a percent)

46.45%

46.45%

46.45%

General Partner

Distributions

Incentive distributions

1

0

0

Common Units (Limited Partners)

Distributions

Partnership distribution

188

169

Number of common units

63,561,546

62,327,766

63,561,546

62,327,766

53,472,766

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

Distributions

Number of common units

5,797,106

5,797,106

Common Units (Limited Partners) | TransCanada

Distributions

Number of common units

11,287,725

11,287,725

General Partner | TC PipeLines GP, Inc.

Distributions

Ownership interest in the Partnership (as a percent)

2.00%

2.00%

2.00%

2.00%

2.00%

Subsequent event

Distributions

Cash distribution (in dollars per unit)

$0.84

Subsequent event | GTN

Distributions

Distribution received by Partnership

21

Subsequent event | GTN

Distributions

Aggregate distribution declared and payable by investee

31

Subsequent event | General Partner

Distributions

Incentive distributions

0

Subsequent event | General Partner | TC PipeLines GP, Inc.

Distributions

Partnership distribution

1

Subsequent event | Distribution declared | Northern Border

Distributions

Partnership distribution

43

Subsequent event | Distribution declared | Great Lakes

Distributions

Partnership distribution

17

Subsequent event | Cash Distribution Paid

Distributions

Partnership distribution

55

Subsequent event | Cash Distribution Paid | Northern Border

Distributions

Partnership's share of distributions

21

Subsequent event | Cash Distribution Paid | Great Lakes

Distributions

Partnership's share of distributions

8

Subsequent event | Cash Distribution Paid | Common Units (Limited Partners)

Distributions

Partnership distribution

54

Subsequent event | Cash Distribution Paid | Common Units (Limited Partners) | TC PipeLines GP, Inc.

Distributions

Partnership distribution

5

Subsequent event | Cash Distribution Paid | Common Units (Limited Partners) | TransCanada

Distributions

Partnership distribution

$9

SUBSEQUENT_EVENTS_Details_2

SUBSEQUENT EVENTS (Details 2) (GTN, Former parent, TransCanada subsidiaries, Transaction between entities under common control, USD $)	0 Months Ended
In Millions, unless otherwise specified	Jul. 01, 2013	Feb. 24, 2015
Subsequent events
Interest acquired (as a percent)	45.00%
Purchase price	$750
Assumption of proportional debt	146
Subsequent event | Expected
Subsequent events
Interest acquired (as a percent)		30.00%
Purchase price		446
Total cash consideration		253
Assumption of proportional debt		98
Subsequent event | Partnership interest | Class B units | Expected
Subsequent events
Equity issuance		95
Portion of GTN's annual distributions to which the Class B units are entitled to receive a percentage share of the distributions above $20 million (as a percent)		30.00%
Period for payment of 30 percent of GTN's distributions above $20 million at 100 percent		5 years
Percentage applied to 30 percent of GTN's distributions above $20 million for the first five years		100.00%
Threshold of 30 percent of GTN's annual distributions for payment to Class B units at specified percentage		$20
Percentage applied to 30 percent of GTN's distributions above $20 million after the first five years		25.00%