EQUITY INVESTMENTS (Details) - USD ($) $ in Millions		1 Months Ended		3 Months Ended								12 Months Ended
	Dec. 31, 2015	Aug. 31, 2016	Apr. 30, 2006	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jan. 01, 2016
EQUITY INVESTMENTS
Equity Earnings				$ 28	$ 24	$ 22	$ 42	$ 34	$ 17	$ 15	$ 31	$ 116	$ 97	$ 88
Equity Investments	$ 965			1,044				965				1,044	965
Impairment of equity-method investment								199					199
LIABILITIES AND PARTNERS' EQUITY
Current portion of long-term debt	14			23				14				23	14
Amount borrowed												209	618	35
Nonrecurring fair value measurement
EQUITY INVESTMENTS
Impairment of equity-method investment												$ 0	0	0
Northern Border
EQUITY INVESTMENTS
Partnership interest held (as a percent)												50.00%
LIABILITIES AND PARTNERS' EQUITY
Current portion of long-term debt		$ 100
Northern Border | Revolving credit facility | Revolving Credit Agreement Expiring 2020
LIABILITIES AND PARTNERS' EQUITY
Amount borrowed		$ 200
Great Lakes
EQUITY INVESTMENTS
Partnership interest held (as a percent)												46.45%
Total cash call issued to fund debt repayment				10			9	10			$ 9
LIABILITIES AND PARTNERS' EQUITY
Current portion of long-term debt	19			$ 19				19				$ 19	19
Northern Border
EQUITY INVESTMENTS
Ownership interest (as a percent)				50.00%								50.00%
Equity Earnings												$ 69	66	69
Equity Investments	480			$ 444				480				$ 444	480
Amortization period of transaction fee			12 years
Transaction fee			$ 10
Additional ownership interest acquired (as a percent)			20.00%
Ownership interest (as a percent)				50.00%								50.00%
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	116			$ 116				116				116	116
Assets
Cash and cash equivalents	27			14				27				14	27
Other current assets	33			36				33				36	33
Plant, property and equipment, net	1,124			1,089				1,124				1,089	1,124
Other assets	16			14				16				14	16
Assets, total	1,200			1,153				1,200				1,153	1,200
LIABILITIES AND PARTNERS' EQUITY
Current liabilities	39			38				39				38	39
Deferred credits and other	26			28				26				28	26
Long-term debt, net	409			430				409				430	409
Partners' equity
Partners' equity	728			659				728				659	728
Accumulated other comprehensive loss	(2)			(2)				(2)				(2)	(2)
Liabilities and Partners' Equity, total	1,200			$ 1,153				$ 1,200				1,153	1,200
Revenues (expenses)
Transmission revenues												292	286	293
Operating expenses												(72)	(70)	(72)
Depreciation												(59)	(60)	(59)
Financial charges and other												(21)	(22)	(22)
Net income												140	$ 134	140
Northern Border | Nonrecurring fair value measurement
EQUITY INVESTMENTS
Impairment of equity-method investment	$ 0											$ 0
Northern Border | ONEOK Partners, L.P.
EQUITY INVESTMENTS
Ownership interest (as a percent)				50.00%								50.00%
Great Lakes
EQUITY INVESTMENTS
Ownership interest (as a percent)	46.45%			46.45%				46.45%			46.45%	46.45%	46.45%
Equity Earnings												$ 28	$ 31	19
Equity Investments	$ 485			$ 474				$ 485				474	485
Undistributed earnings												0	0	0
Equity contribution				5			$ 4	5			$ 4	9	9	9
Assets
Current assets	86			66				86				66	86
Plant, property and equipment, net	727			714				727				714	727
Assets, total	813			780				813				780	813
LIABILITIES AND PARTNERS' EQUITY
Current liabilities	31			40				31				40	31
Long-term debt, net	297			278				297				278	297
Partners' equity
Partners' equity	485			462				485				462	485
Liabilities and Partners' Equity, total	813			$ 780				813				780	813
Revenues (expenses)
Transmission revenues												179	177	146
Operating expenses												(69)	(59)	(53)
Depreciation												(28)	(28)	(28)
Financial charges and other												(21)	(23)	(25)
Net income												$ 61	67	$ 40
Great Lakes | Nonrecurring fair value measurement
EQUITY INVESTMENTS
Impairment of equity-method investment								199					199
Amount of difference between the carrying value and the underlying equity in net assets resulting from the recognition and inclusion of goodwill	260							260					260
Great Lakes | TransCanada
EQUITY INVESTMENTS
Ownership interest (as a percent)				53.55%								53.55%
Portland Natural Gas Transmission System
EQUITY INVESTMENTS
Ownership interest (as a percent)				49.90%								49.90%			49.90%
Equity Earnings												$ 19
Equity Investments				$ 126								$ 126
TC PipeLines Intermediate Limited Partnership
EQUITY INVESTMENTS
Partnership interest held (as a percent)												98.9899%
TC GL Intermediate Limited Partnership
EQUITY INVESTMENTS
Partnership interest held (as a percent)												98.9899%
ASU 2015-03, Interest - Imputation of Interest | Adjustment | Northern Border
Assets
Other assets	(2)							(2)					(2)
LIABILITIES AND PARTNERS' EQUITY
Long-term debt, net	$ (2)							$ (2)					$ (2)