INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended							3 Months Ended		12 Months Ended				12 Months Ended	0 Months Ended	1 Months Ended	12 Months Ended							12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2012 TC GL Intermediate Limited Partnership	Dec. 31, 2012 TC PipeLines Intermediate Limited Partnership	Dec. 31, 2012 Great Lakes	Mar. 31, 2012 Great Lakes	Dec. 31, 2012 Great Lakes	Dec. 31, 2011 Great Lakes	Dec. 31, 2010 Great Lakes	Feb. 28, 2007 Great Lakes	Dec. 31, 2012 Great Lakes TransCanada Corporation	Jan. 02, 2013 Northern Border	Apr. 30, 2006 Northern Border	Dec. 31, 2012 Northern Border	Dec. 31, 2011 Northern Border	Dec. 31, 2010 Northern Border	Dec. 31, 2012 Northern Border ONEOK Partners L.P.	Dec. 31, 2012 GTN	Dec. 31, 2011 GTN	May 03, 2011 GTN	Dec. 31, 2012 Bison	Dec. 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%			46.45%				50.00%				25.00%		25.00%	25.00%		25.00%
Partnership interest held (as a percent)														98.9899%	98.9899%
Equity income	$ 29	$ 31	$ 31	$ 38	$ 38	$ 40	$ 37	$ 39	$ 129	[1]	$ 154	[1]	$ 126					$ 27	$ 60	$ 59					$ 72	$ 75	$ 67		$ 19	$ 12		$ 11	$ 7
Undistributed earnings																																	1
Investment in Unconsolidated Affiliates	1,563				1,610				1,563		1,610					677		677	686						512	536			216	225		158	163
Amortization period of transaction fee																									12 years
Transaction fee																								10
Additional ownership interest acquired (as a percent)																								20.00%
Limited partnership interest (as a percent)																						53.55%						50.00%
Amount of difference between the carrying value and the underlying equity in net assets resulting from the recognition and inclusion of goodwill																458		458	458						119	120
Equity contribution																5	4	9	9	9						55
Total cash call issued to fund debt repayment																10	9
Assets
Current assets																56		56	65										50	55		7	10
Cash and cash equivalents																									28	33
Other current assets																									35	35
Plant, property and equipment, net																799		799	826						1,234	1,267			1,174	1,207		649	658
Other assets																			1						31	31			1	1
Assets, total																855		855	892						1,328	1,366			1,225	1,263		656	668
Liabilities and Partners' Equity
Current liabilities																30		30	30						53	48			16	18		25	17
Deferred credits and other																									16	13			20	20
Long-term debt, including current maturities																354		354	373						473	473			325	325
Partners' equity
Partners' equity																471		471	489						789	835			864	900		631	651
Accumulated other comprehensive loss																									(3)	(3)
Liabilities and Equity, total																855		855	892						1,328	1,366			1,225	1,263		656	668
Revenues (expenses)
Transmission revenues																		182	250	262					311	310	295		198	133		80	52
Operating expenses																		(66)	(62)	(59)					(79)	(73)	(74)		(48)	(37)		(16)	(11)
Depreciation																		(31)	(32)	(40)					(63)	(62)	(62)		(54)	(36)		(19)	(13)
Financial charges and other																		(28)	(30)	(31)					(24)	(22)	(23)		(18)	(15)
Michigan business tax																			2	(5)
Net income																		$ 57	$ 128	$ 127					$ 145	$ 153	$ 136		$ 78	$ 45		$ 45	$ 28
Reduction in current transportation rates (as a percent)																							11.00%

[1] 25 percent interests in each of GTN and Bison were acquired in May 2011.