INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended					3 Months Ended			1 Months Ended	3 Months Ended			3 Months Ended				3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011		Dec. 31, 2011	Mar. 31, 2012 Great Lakes	Mar. 31, 2011 Great Lakes	Dec. 31, 2011 Great Lakes	Apr. 30, 2006 Northern Border	Mar. 31, 2012 Northern Border Y	Mar. 31, 2011 Northern Border	Dec. 31, 2011 Northern Border	Mar. 31, 2012 GTN	Dec. 31, 2011 GTN	May 31, 2011 GTN	May 03, 2011 GTN	Mar. 31, 2012 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%				50.00%			25.00%		25.00%	25.00%	25.00%		25.00%	25.00%
Equity income	$ 38	[1]	$ 39	[1]		$ 9	$ 18			$ 20	$ 21		$ 6				$ 3
Investment in Unconsolidated Affiliates	1,606				1,610	688		686		531		536	225	225			162	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						65		65					66	55			7	10
Cash and cash equivalents										39		33
Other current assets										37		35
Plant, property and equipment, net						819		826		1,255		1,267	1,197	1,207			656	658
Other assets						1		1		30		31	2	1
Assets, total						885		892		1,361		1,366	1,265	1,263			663	668
Liabilities and Partners' Equity
Current liabilities						26		30		51		48	18	18			15	17
Deferred credits and other						1				14		13	20	20
Long-term debt, including current maturities						364		373		473		473	325	325
Partners' equity
Partners' capital						494		489		826		835	902	900			648	651
Accumulated other comprehensive loss										(3)		(3)
Liabilities and Equity, total						885		892		1,361		1,366	1,265	1,263			663	668
Revenues (expenses)
Transmission revenues						49	70			81	80		52				20
Operating expenses						(15)	(14)			(18)	(17)		(11)				(3)
Depreciation						(8)	(8)			(16)	(15)		(13)				(5)
Financial charges and other						(7)	(7)			(6)	(6)		(5)
Michigan business tax							(2)
Net income						$ 19	$ 39			$ 41	$ 42		$ 23				$ 12

[1] There were no equity earnings from GTN and Bison in the 2011 period as the 25 percent interests in each were acquired in May 2011.