ORGANIZATION (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Organization
Equity earnings from unconsolidated affiliates (Note 3)	$ 40.4	[1]	$ 35.6	[1]	$ 116.5	[1]	$ 91.8	[1]
Equity Earnings from Unconsolidated Affiliates	$ 40.4	[1]	$ 35.6	[1]	$ 116.5	[1]	$ 91.8	[1]
Great Lakes
Organization
Ownership interest (as a percent)	46.45%				46.45%
Northern Border
Organization
Ownership interest (as a percent)	50.00%				50.00%
GTN
Organization
Ownership interest (as a percent)	25.00%				25.00%
Length of the pipeline owned by equity method investee (in miles)					1,353
Bison
Organization
Ownership interest (as a percent)	25.00%				25.00%
Length of the pipeline owned by equity method investee (in miles)					303
North Baja Pipeline, LLC
Organization
Partnership interest held (as a percent)					100.00%
Tuscarora Gas Transmission Company
Organization
Partnership interest held (as a percent)					100.00%

[1] Includes equity earnings from GTN and Bison from May 3, 2011, date of acquisition, to September 30, 2011.