INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended
	Apr. 30, 2006	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Investments in unconsolidated affiliates
Equity Earnings from Unconsolidated Affiliates		$ 17		$ 15	$ 63	$ 66
Investments in Unconsolidated Affiliates		$ 1,151			1,151		$ 1,177
Equity contribution					$ 4	4
Great Lakes
Investments in unconsolidated affiliates
Total cash call issued to fund debt repayment			$ 9
Northern Border
Investments in unconsolidated affiliates
Ownership interest (as a percent)		50.00%			50.00%
Equity Earnings from Unconsolidated Affiliates		$ 16		14	$ 50	53
Investments in Unconsolidated Affiliates		487			487		505
Amortization period of transaction fee	12 years
Transaction fee	$ 10
Additional ownership interest acquired (as a percent)	20.00%
Assets
Cash and cash equivalents		40			40		41
Other current assets		33			33		34
Plant, property and equipment, net		1,135			1,135		1,163
Other assets		18			18		34
Assets, total		1,226			1,226		1,272
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		50			50		64
Deferred credits and other		25			25		22
Long-term debt, including current maturities		411			411		411
Partners' equity
Partners' equity		742			742		777
Accumulated other comprehensive loss		(2)			(2)		(2)
Liabilities and Partners' Equity, total		1,226			1,226		1,272
Revenues (expenses)
Transmission revenues		71		66	215	221
Operating expenses		(17)		(16)	(51)	(50)
Depreciation		(16)		(15)	(45)	(44)
Financial charges and other		(6)		(8)	(17)	(20)
Net income		$ 32		27	$ 102	107
Great Lakes
Investments in unconsolidated affiliates
Ownership interest (as a percent)		46.45%	46.45%		46.45%
Equity Earnings from Unconsolidated Affiliates		$ 1		1	$ 13	13
Investments in Unconsolidated Affiliates		664			664		672
Equity contribution			$ 4
Assets
Current assets		67			67		66
Plant, property and equipment, net		730			730		748
Assets, total		797			797		814
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		48			48		38
Long-term debt, including current maturities		307			307		316
Partners' equity
Partners' equity		442			442		460
Liabilities and Partners' Equity, total		797			797		$ 814
Revenues (expenses)
Transmission revenues		29		29	105	106
Operating expenses		(15)		(14)	(40)	(38)
Depreciation		(7)		(7)	(21)	(21)
Financial charges and other		(5)		(6)	(17)	(19)
Net income		$ 2		$ 2	$ 27	$ 28