INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended			3 Months Ended			6 Months Ended			0 Months Ended	3 Months Ended		6 Months Ended				3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 Great Lakes	Mar. 31, 2013 Great Lakes	Jun. 30, 2012 Great Lakes	Jun. 30, 2013 Great Lakes	Jun. 30, 2012 Great Lakes	Dec. 31, 2012 Great Lakes	Jan. 02, 2013 Northern Border	Jun. 30, 2013 Northern Border	Jun. 30, 2012 Northern Border	Jun. 30, 2013 Northern Border	Jun. 30, 2012 Northern Border	Dec. 31, 2012 Northern Border	Apr. 30, 2006 Northern Border	Jun. 30, 2013 GTN	Jun. 30, 2012 GTN	Jun. 30, 2013 GTN	Jun. 30, 2012 GTN	Dec. 31, 2012 GTN	Jun. 30, 2013 Bison	Jun. 30, 2012 Bison	Jun. 30, 2013 Bison	Jun. 30, 2012 Bison	Dec. 31, 2012 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%
Equity Earnings from Unconsolidated Affiliates	$ 22	$ 31	$ 48	$ 69				$ 8	$ 2	$ 17			$ 15	$ 16	$ 31	$ 36			$ 4	$ 4	$ 9	$ 10		$ 3	$ 3	$ 6	$ 6
Undistributed earnings									0	0					0	0					0	0				0	0
Investments in Unconsolidated Affiliates	1,545		1,545		1,563	671			671		677		500		500		512		212		212		216	162		162		158
Amortization period of transaction fee															12 years
Transaction fee															10
Additional ownership interest acquired (as a percent)																		20.00%
Equity contribution							4		4	4														6		6
Total cash call issued to fund debt repayment							9																	24
Assets
Current assets						41			41		56								51		51		50	16		16		7
Cash and cash equivalents													31		31		28
Other current assets													33		33		35
Plant, property and equipment, net						784			784		799		1,212		1,212		1,234		1,152		1,152		1,174	640		640		649
Other assets													30		30		31		1		1		1
Assets, total						825			825		855		1,306		1,306		1,328		1,204		1,204		1,225	656		656		656
LIABILITIES AND PARTNERS' EQUITY
Current liabilities						22			22		30		52		52		53		13		13		16	7		7		25
Deferred credits and other													18		18		16		21		21		20
Long-term debt, including current maturities						345			345		354		473		473		473		325		325		325
Partners' equity
Partners' equity						458			458		471		765		765		789		845		845		864	649		649		631
Accumulated other comprehensive loss													(2)		(2)		(3)
Liabilities and Equity, total						825			825		855		1,306		1,306		1,328		1,204		1,204		1,225	656		656		656
Revenues (expenses)
Transmission revenues						29		48	64	97			69	73	141	154			46	48	95	100		20	20	40	40
Operating expenses						(15)		(16)	(30)	(31)			(19)	(18)	(38)	(36)			(12)	(13)	(23)	(24)		(4)	(4)	(8)	(7)
Depreciation						(8)		(8)	(16)	(16)			(14)	(16)	(29)	(32)			(14)	(14)	(27)	(27)		(5)	(5)	(10)	(10)
Financial charges and other						(7)		(7)	(14)	(14)			(6)	(7)	(11)	(13)			(5)	(4)	(9)	(9)
Net income/(loss)						$ (1)		$ 17	$ 4	$ 36			$ 30	$ 32	$ 63	$ 73			$ 15	$ 17	$ 36	$ 40		$ 11	$ 11	$ 22	$ 23
Reduction in current transportation rates (as a percent)												11.00%