INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended					1 Months Ended	0 Months Ended
	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)									98.9899%
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)									98.9899%

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