SUBSEQUENT EVENTS (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended																12 Months Ended					0 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, 2010	Dec. 31, 2012 Great Lakes	Feb. 28, 2007 Great Lakes	Dec. 31, 2012 Northern Border	Dec. 31, 2012 GTN	May 03, 2011 GTN	Dec. 31, 2012 Bison	May 03, 2011 Bison	Dec. 31, 2012 General Partner	Dec. 31, 2012 TransCanada Corporation	Dec. 31, 2012 Great Lakes	Dec. 31, 2012 GTN	Dec. 31, 2012 Bison	Jan. 17, 2013 Subsequent event Cash distribution declared	Jan. 11, 2013 Subsequent event Cash distribution declared Great Lakes	Feb. 01, 2013 Subsequent event Cash distribution declared Northern Border	Jan. 11, 2013 Subsequent event Cash distribution declared GTN	Jan. 11, 2013 Subsequent event Cash distribution declared Bison	Feb. 14, 2013 Subsequent event Cash Distribution Paid	Feb. 01, 2013 Subsequent event Cash Distribution Paid Great Lakes	Feb. 01, 2013 Subsequent event Cash Distribution Paid Northern Border	Feb. 01, 2013 Subsequent event Cash Distribution Paid GTN	Feb. 01, 2013 Subsequent event Cash Distribution Paid Bison	Feb. 14, 2013 Subsequent event Cash Distribution Paid Common unitholders	Feb. 14, 2013 Subsequent event Cash Distribution Paid Common units held by General Partner	Feb. 14, 2013 Subsequent event Cash Distribution Paid General Partner	Jan. 29, 2013 Subsequent event Cash Distribution Paid General Partner	Feb. 14, 2013 Subsequent event Cash Distribution Paid TransCanada Corporation	Jan. 29, 2013 Subsequent event Cash Distribution Paid TransCanada Corporation
Subsequent events
Cash distribution (in dollars per unit)																						$ 0.78
Cash distribution paid	$ 43	$ 43	$ 42	$ 42	$ 42	$ 42	$ 35	$ 35																			$ 43					$ 42	$ 5	$ 1		$ 9
Aggregate distribution declared and payable by investee																							14	43	22	15
Number of common units owned	53,500,000				53,500,000				46,200,000								5,797,106	11,287,725																	5,797,106		11,287,725
Ownership interest (as a percent)										46.45%	46.45%	50.00%	25.00%	25.00%	25.00%	25.00%			46.45%	25.00%	25.00%							46.45%	50.00%	25.00%	25.00%
General partner ownership interest in the partnership (as a percent)																	2.00%																		2.00%
Partnership's share of distributions declared and payable by investee																												$ 6	$ 22	$ 6	$ 4