INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Details) (USD $)	0 Months Ended	1 Months Ended	3 Months Ended
	Jan. 02, 2013	Apr. 30, 2006	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Investments in unconsolidated affiliates
Equity Earnings from Unconsolidated Affiliates			$ 26,000,000	$ 38,000,000
Investments in Unconsolidated Affiliates			1,556,000,000		1,563,000,000
Great Lakes
Investments in unconsolidated affiliates
Ownership interest at the end of the period (as a percent)			46.45%
Equity Earnings from Unconsolidated Affiliates			2,000,000	9,000,000
Undistributed earnings			0	0
Investments in Unconsolidated Affiliates			677,000,000		677,000,000
Equity contribution			4,000,000	4,000,000
Total cash call issued to fund debt repayment			9,000,000
Assets
Current assets			51,000,000		56,000,000
Plant, property and equipment, net			792,000,000		799,000,000
Assets, total			843,000,000		855,000,000
Liabilities and Partners' Equity
Current liabilities			27,000,000		30,000,000
Long-term debt, including current maturities			345,000,000		354,000,000
Partners' equity
Partners' equity			471,000,000		471,000,000
Liabilities and Equity, total			843,000,000		855,000,000
Revenues (expenses)
Transmission revenues			35,000,000	49,000,000
Operating expenses			(15,000,000)	(15,000,000)
Depreciation			(8,000,000)	(8,000,000)
Financial charges and other			(7,000,000)	(7,000,000)
Net income			5,000,000	19,000,000
Northern Border
Investments in unconsolidated affiliates
Ownership interest at the end of the period (as a percent)			50.00%
Equity Earnings from Unconsolidated Affiliates			16,000,000	20,000,000
Undistributed earnings			0	0
Investments in Unconsolidated Affiliates			507,000,000		512,000,000
Amortization period of transaction fee			12 years
Transaction fee		10,000,000
Additional ownership interest acquired (as a percent)		20.00%
Assets
Cash and cash equivalents			34,000,000		28,000,000
Other current assets			34,000,000		35,000,000
Plant, property and equipment, net			1,220,000,000		1,234,000,000
Other assets			31,000,000		31,000,000
Assets, total			1,319,000,000		1,328,000,000
Liabilities and Partners' Equity
Current liabilities			53,000,000		53,000,000
Deferred credits and other			17,000,000		16,000,000
Long-term debt, including current maturities			473,000,000		473,000,000
Partners' equity
Partners' equity			779,000,000		789,000,000
Accumulated other comprehensive loss			(3,000,000)		(3,000,000)
Liabilities and Equity, total			1,319,000,000		1,328,000,000
Revenues (expenses)
Transmission revenues			72,000,000	81,000,000
Operating expenses			(19,000,000)	(18,000,000)
Depreciation			(15,000,000)	(16,000,000)
Financial charges and other			(5,000,000)	(6,000,000)
Net income			33,000,000	41,000,000
Reduction in current transportation rates (as a percent)	11.00%
GTN
Investments in unconsolidated affiliates
Ownership interest at the end of the period (as a percent)			25.00%
Equity Earnings from Unconsolidated Affiliates			5,000,000	6,000,000
Undistributed earnings			0	0
Investments in Unconsolidated Affiliates			215,000,000		216,000,000
Assets
Current assets			62,000,000		50,000,000
Plant, property and equipment, net			1,162,000,000		1,174,000,000
Other assets			1,000,000		1,000,000
Assets, total			1,225,000,000		1,225,000,000
Liabilities and Partners' Equity
Current liabilities			17,000,000		16,000,000
Deferred credits and other			21,000,000		20,000,000
Long-term debt, including current maturities			325,000,000		325,000,000
Partners' equity
Partners' equity			862,000,000		864,000,000
Liabilities and Equity, total			1,225,000,000		1,225,000,000
Revenues (expenses)
Transmission revenues			49,000,000	52,000,000
Operating expenses			(11,000,000)	(11,000,000)
Depreciation			(13,000,000)	(13,000,000)
Financial charges and other			(4,000,000)	(5,000,000)
Net income			21,000,000	23,000,000
Bison
Investments in unconsolidated affiliates
Ownership interest at the end of the period (as a percent)			25.00%
Equity Earnings from Unconsolidated Affiliates			3,000,000	3,000,000
Undistributed earnings			0	0
Investments in Unconsolidated Affiliates			157,000,000		158,000,000
Assets
Current assets			7,000,000		7,000,000
Plant, property and equipment, net			645,000,000		649,000,000
Assets, total			652,000,000		656,000,000
Liabilities and Partners' Equity
Current liabilities			25,000,000		25,000,000
Partners' equity
Partners' equity			627,000,000		631,000,000
Liabilities and Equity, total			652,000,000		656,000,000
Revenues (expenses)
Transmission revenues			20,000,000	20,000,000
Operating expenses			(4,000,000)	(3,000,000)
Depreciation			(5,000,000)	(5,000,000)
Net income			$ 11,000,000	$ 12,000,000