INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended
	Apr. 30, 2006	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Investments in unconsolidated affiliates
Equity Earnings from Unconsolidated Affiliates		$ 15		$ 18	$ 46	$ 51
Investments in Unconsolidated Affiliates		$ 1,158			1,158		$ 1,177
Equity contribution					$ 4	4
Northern Border
Investments in unconsolidated affiliates
Transaction fee	$ 10
Interest acquired by Partnership (as a percent)	20.00%
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		$ 15		16	$ 34	39
Investments in Unconsolidated Affiliates		492			492		505
Amortization period of transaction fee	12 years
Assets
Cash and cash equivalents		40			40		41
Other current assets		32			32		34
Plant, property and equipment, net		1,142			1,142		1,163
Other assets		34			34		34
Assets, total		1,248			1,248		1,272
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		63			63		64
Deferred credits and other		24			24		22
Long-term debt, including current maturities		411			411		411
Partners' equity
Partners' equity		752			752		777
Accumulated other comprehensive loss		(2)			(2)		(2)
Liabilities and Partners' Equity, total		1,248			1,248		1,272
Revenues (expenses)
Transmission revenues		69		69	144	155
Operating expenses		(18)		(16)	(34)	(34)
Depreciation		(14)		(15)	(29)	(30)
Financial charges and other		(6)		(6)	(11)	(12)
Net income		$ 31		32	$ 70	79
Great Lakes
Investments in unconsolidated affiliates
Ownership interest (as a percent)		46.45%	46.45%		46.45%
Equity Earnings from Unconsolidated Affiliates				2	$ 12	12
Investments in Unconsolidated Affiliates		$ 666			666		672
Equity contribution			$ 4
Assets
Current assets		70			70		66
Plant, property and equipment, net		736			736		748
Assets, total		806			806		814
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		52			52		38
Long-term debt, including current maturities		307			307		316
Partners' equity
Partners' equity		447			447		460
Liabilities and Partners' Equity, total		806			806		$ 814
Revenues (expenses)
Transmission revenues		28		29	76	77
Operating expenses		(14)		(12)	(25)	(24)
Depreciation		(7)		(7)	(14)	(14)
Financial charges and other		(6)		(6)	(12)	(13)
Net income		$ 1		$ 4	$ 25	$ 26