INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended					0 Months Ended	9 Months Ended		3 Months Ended			9 Months Ended			1 Months Ended	3 Months Ended		9 Months Ended			3 Months Ended		5 Months Ended	9 Months Ended				3 Months Ended		5 Months Ended	9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Dec. 31, 2011	Sep. 27, 2012 Northern Border Y	Sep. 30, 2012 Northern Border	Nov. 02, 2012 Northern Border	Sep. 30, 2012 Great Lakes	Mar. 31, 2012 Great Lakes	Sep. 30, 2011 Great Lakes	Sep. 30, 2012 Great Lakes	Sep. 30, 2011 Great Lakes	Dec. 31, 2011 Great Lakes	Apr. 30, 2006 Northern Border	Sep. 30, 2012 Northern Border Y	Sep. 30, 2011 Northern Border	Sep. 30, 2012 Northern Border	Sep. 30, 2011 Northern Border	Dec. 31, 2011 Northern Border	Sep. 30, 2012 GTN	Sep. 30, 2011 GTN	Sep. 30, 2011 GTN	Sep. 30, 2012 GTN	Sep. 30, 2011 GTN	Dec. 31, 2011 GTN	May 03, 2011 GTN	Sep. 30, 2012 Bison	Sep. 30, 2011 Bison	Sep. 30, 2011 Bison	Sep. 30, 2012 Bison	Sep. 30, 2011 Bison	Dec. 31, 2011 Bison	May 03, 2011 Bison
Investments in unconsolidated affiliates
Ownership interest at the end of the period (as a percent)												50.00%	46.45%			46.45%				50.00%		50.00%			25.00%			25.00%			25.00%	25.00%			25.00%			25.00%
Equity income	$ 31	[1]	$ 40	[1]	$ 100	[1]	$ 116	[1]					$ 6		$ 14	$ 23	$ 49			$ 18	$ 19	$ 54	$ 56		$ 5	$ 5		$ 15	$ 7			$ 2	$ 2		$ 8	$ 4
Investment in Unconsolidated Affiliates	1,576				1,576				1,610				679			679		686		519		519		536	219			219		225		159			159		163
Amortization period of transaction fee (in years)																				12
Transaction fee																			10
Additional ownership interest acquired (as a percent)																			20.00%
Equity contribution														4		4	4						50
Total cash call issued by Great Lakes to fund its debt repayment														9
Assets
Current assets													56			56		65							62			62		55		7			7		10
Cash and cash equivalents																				35		35		33
Other current assets																				36		36		35
Plant, property and equipment, net													805			805		826		1,237		1,237		1,267	1,174			1,174		1,207		650			650		658
Other assets													1			1		1		30		30		31	1			1		1
Assets, total													862			862		892		1,338		1,338		1,366	1,237			1,237		1,263		657			657		668
Liabilities and Partners' Equity
Current liabilities													23			23		30		51		51		48	17			17		18		20			20		17
Deferred credits and other																				16		16		13	20			20		20
Long-term debt, including current maturities													364			364		373		473		473		473	325			325		325
Partners' equity
Partners' equity													475			475		489		801		801		835	875			875		900		637			637		651
Accumulated other comprehensive loss																				(3)		(3)		(3)
Liabilities and Equity, total													862			862		892		1,338		1,338		1,366	1,237			1,237		1,263		657			657		668
Revenues (expenses)
Transmission revenues													46		63	143	196			78	77	232	230		47	50		147	83			20	18		60	32
Operating expenses													(17)		(16)	(48)	(46)			(21)	(17)	(57)	(53)		(11)	(14)		(35)	(23)			(4)	(6)		(11)	(9)
Depreciation													(8)		(8)	(24)	(24)			(16)	(15)	(48)	(46)		(14)	(9)		(41)	(15)			(5)	(5)		(15)	(8)
Financial charges and other													(7)		(7)	(21)	(22)			(5)	(6)	(18)	(17)		(4)	(4)		(13)	(10)
Michigan business tax															(1)		2
Net income													14		31	50	106			36	39	109	114		18	23		58	35			11	7		34	15
Decrease in long-term transportation rate (as a percent)										11.00%
Moratorium period (in years)										3
Composite depreciation rate (as a percent)											2.40%
Composite depreciation rate, Northern Border Settlement, if approved (as a percent)										2.19%
Undistributed earnings																											$ 7							$ 4

[1] 25 percent interests in each of GTN and Bison were acquired in May 2011.