INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended			3 Months Ended			6 Months Ended			1 Months Ended	3 Months Ended		6 Months Ended			2 Months Ended	3 Months Ended		6 Months Ended					2 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Jun. 30, 2012 Great Lakes	Mar. 31, 2012 Great Lakes	Jun. 30, 2011 Great Lakes	Jun. 30, 2012 Great Lakes	Jun. 30, 2011 Great Lakes	Dec. 31, 2011 Great Lakes	Apr. 30, 2006 Northern Border	Jun. 30, 2012 Northern Border Y	Jun. 30, 2011 Northern Border	Jun. 30, 2012 Northern Border	Jun. 30, 2011 Northern Border	Dec. 31, 2011 Northern Border	Jun. 30, 2011 GTN	Jun. 30, 2012 GTN	Jun. 30, 2011 GTN	Jun. 30, 2012 GTN	Jun. 30, 2011 GTN	Dec. 31, 2011 GTN	May 31, 2011 GTN	May 03, 2011 GTN	Jun. 30, 2011 Bison	Jun. 30, 2012 Bison	Jun. 30, 2011 Bison	Jun. 30, 2012 Bison	Jun. 30, 2011 Bison	Dec. 31, 2011 Bison	May 31, 2011 Bison	May 03, 2011 Bison
Investments in unconsolidated affiliates
Ownership interest at the end of the period (as a percent)						46.45%			46.45%				50.00%		50.00%				25.00%		25.00%			25.00%	25.00%		25.00%		25.00%			25.00%	25.00%
Equity income	$ 31	$ 37	$ 69	$ 76		$ 8		$ 17	$ 17	$ 35			$ 16	$ 16	$ 36	$ 37			$ 4	$ 2	$ 10	$ 2					$ 3	$ 2	$ 6	$ 2
Investment in Unconsolidated Affiliates	1,586		1,586		1,610	683			683		686		521		521		536		222		222		225				160		160		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
Total cash call issued by Great Lakes to fund its debt repayment							9
Assets
Current assets						62			62		65								65		65		55				7		7		10
Cash and cash equivalents													30		30		33
Other current assets													33		33		35
Plant, property and equipment, net						812			812		826		1,248		1,248		1,267		1,186		1,186		1,207				652		652		658
Other assets						1			1		1		31		31		31		1		1		1
Assets, total						875			875		892		1,342		1,342		1,366		1,252		1,252		1,263				659		659		668
Liabilities and Partners' Equity
Current liabilities						27			27		30		47		47		48		21		21		18				18		18		17
Deferred credits and other													15		15		13		20		20		20
Long-term debt, including current maturities						364			364		373		478		478		473		325		325		325
Partners' equity
Partners' equity						484			484		489		805		805		835		886		886		900				641		641		651
Accumulated other comprehensive loss													(3)		(3)		(3)
Liabilities and Equity, total						875			875		892		1,342		1,342		1,366		1,252		1,252		1,263				659		659		668
Revenues (expenses)
Transmission revenues						48		63	97	133			73	73	154	153			48	33	100	33					20	14	40	14
Operating expenses						(16)		(16)	(31)	(30)			(18)	(19)	(36)	(36)			(13)	(9)	(24)	(9)					(4)	(3)	(7)	(3)
Depreciation						(8)		(8)	(16)	(16)			(16)	(16)	(32)	(31)			(14)	(6)	(27)	(6)					(5)	(3)	(10)	(3)
Financial charges and other						(7)		(8)	(14)	(15)			(7)	(5)	(13)	(11)			(4)	(6)	(9)	(6)
Michigan business tax								5		3
Net income						17		36	36	75			32	33	73	75			17	12	40	12					11	8	23	8
Undistributed earnings																		$ 2								$ 2