INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Details) - USD ($) $ in Millions				1 Months Ended	3 Months Ended								12 Months Ended
		Dec. 31, 2015	Nov. 14, 2013	Apr. 30, 2006	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013		Feb. 28, 2007
Investments in unconsolidated affiliates
Equity Earnings from Unconsolidated Affiliates					$ 34	$ 17	$ 15	$ 31	$ 22	$ 15	$ 18	$ 33	$ 97	$ 88	$ 67	[1]
Investment in Unconsolidated Affiliates		$ 965			965				1,177				965	1,177
Impairment charge recognized on equity method investment					199								$ 199
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%								50.00%
Equity Earnings from Unconsolidated Affiliates													$ 66	69	64
Investment in Unconsolidated Affiliates		$ 480			$ 480				505				480	505
Amortization period of transaction fee				12 years
Transaction fee				$ 10
Additional ownership interest acquired (as a percent)				20.00%
Undistributed earnings													0	0	0
Equity contribution	[1]														31
Amount of difference between the carrying value and the underlying equity in net assets resulting from the recognition and inclusion of goodwill		117			117				117				117	117
Assets
Cash and cash equivalents		27			27				41				27	41
Other current assets		33			33				34				33	34
Plant, property and equipment, net		1,124			1,124				1,163				1,124	1,163
Other assets		18			18				34				18	34
Assets, total		1,202			1,202				1,272				1,202	1,272
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		39			39				64				39	64
Deferred credits and other		26			26				22				26	22
Long-term debt, including current maturities		411			411				411				411	411
Partners' equity
Partners' equity		728			728				777				728	777
Accumulated other comprehensive loss		(2)			(2)				(2)				(2)	(2)
Liabilities and Partners' Equity, total		1,202			$ 1,202				1,272				1,202	1,272
Revenues (expenses)
Transmission revenues													286	293	286
Operating expenses													(70)	(72)	(75)
Depreciation													(60)	(59)	(58)
Financial charges and other													(22)	(22)	(23)
Net income													$ 134	140	130
Northern Border | Nonrecurring fair value measurement
Investments in unconsolidated affiliates
Impairment charge recognized on equity method investment		$ 0
Northern Border | ONEOK Partners, L.P.
Investments in unconsolidated affiliates
Ownership interest (as a percent)		50.00%			50.00%								50.00%
Great Lakes
Investments in unconsolidated affiliates
Ownership interest (as a percent)		46.45%			46.45%			46.45%					46.45%				46.45%
Equity Earnings from Unconsolidated Affiliates													$ 31	19	3
Investment in Unconsolidated Affiliates		$ 485			$ 485				672				485	672
Undistributed earnings													0	0	0
Equity contribution					5			$ 4					9	9	9	[1]
Amount of difference between the carrying value and the underlying equity in net assets resulting from the recognition and inclusion of goodwill		260			260				458				260	458
Assets
Current assets		86			86				66				86	66
Plant, property and equipment, net		727			727				748				727	748
Assets, total		813			813				814				813	814
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		31			31				38				31	38
Long-term debt, including current maturities		297			297				316				297	316
Partners' equity
Partners' equity		485			485				460				485	460
Liabilities and Partners' Equity, total		$ 813			813				$ 814				813	814
Revenues (expenses)
Transmission revenues													177	146	124
Operating expenses													(59)	(53)	(60)
Depreciation													(28)	(28)	(31)
Financial charges and other													(23)	(25)	(27)
Net income													$ 67	$ 40	$ 6
Great Lakes | Nonrecurring fair value measurement
Investments in unconsolidated affiliates
Impairment charge recognized on equity method investment					$ 199
Great Lakes | TransCanada
Investments in unconsolidated affiliates
Ownership interest (as a percent)		53.55%			53.55%								53.55%
Great Lakes | Level 3 | Nonrecurring fair value measurement
Investments in unconsolidated affiliates
Fair value of investment		$ 465			$ 465								$ 465
TC PipeLines Intermediate Limited Partnership
Investments in unconsolidated affiliates
Partnership interest held (as a percent)													98.9899%
TC GL Intermediate Limited Partnership
Investments in unconsolidated affiliates
Partnership interest held (as a percent)													98.9899%

[1] Recast as discussed in Note 2 and Note 6.