RELATED PARTY TRANSACTIONS (Details) (USD $) In Millions, unless otherwise specified			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended
	May 31, 2011 GTN	May 31, 2011 Bison	Jun. 30, 2012 General Partner	Jun. 30, 2011 General Partner	Jun. 30, 2012 General Partner	Jun. 30, 2011 General Partner	Jun. 30, 2012 TransCanada Corporation Great Lakes	Jun. 30, 2011 TransCanada Corporation Great Lakes	Jun. 30, 2012 TransCanada Corporation Great Lakes	Jun. 30, 2011 TransCanada Corporation Great Lakes	Dec. 31, 2011 TransCanada Corporation Great Lakes	Jun. 30, 2012 TransCanada Corporation Northern Border	Jun. 30, 2011 TransCanada Corporation Northern Border	Jun. 30, 2012 TransCanada Corporation Northern Border	Jun. 30, 2011 TransCanada Corporation Northern Border	Dec. 31, 2011 TransCanada Corporation Northern Border	Jun. 30, 2012 TransCanada Corporation GTN	Jun. 30, 2011 TransCanada Corporation GTN	Jun. 30, 2012 TransCanada Corporation GTN	Jun. 30, 2011 TransCanada Corporation GTN	Dec. 31, 2011 TransCanada Corporation GTN	Jun. 30, 2012 TransCanada Corporation Bison	Jun. 30, 2011 TransCanada Corporation Bison	Jun. 30, 2012 TransCanada Corporation Bison	Jun. 30, 2011 TransCanada Corporation Bison	Dec. 31, 2011 TransCanada Corporation Bison	Jun. 30, 2012 TransCanada Corporation North Baja	Jun. 30, 2011 TransCanada Corporation North Baja	Jun. 30, 2012 TransCanada Corporation North Baja	Jun. 30, 2011 TransCanada Corporation North Baja	Dec. 31, 2011 TransCanada Corporation North Baja	Jun. 30, 2012 TransCanada Corporation Tuscarora Gas Transmission Company	Jun. 30, 2011 TransCanada Corporation Tuscarora Gas Transmission Company	Jun. 30, 2012 TransCanada Corporation Tuscarora Gas Transmission Company	Jun. 30, 2011 TransCanada Corporation Tuscarora Gas Transmission Company	Dec. 31, 2011 TransCanada Corporation Tuscarora Gas Transmission Company
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates					$ 1	$ 1	$ 8	$ 7	$ 16	$ 15		$ 7	$ 7	$ 15	$ 14		$ 7	$ 6	$ 14	$ 6		$ 1	$ 2	$ 3	$ 2		$ 1	$ 1	$ 2	$ 2		$ 1	$ 1	$ 2	$ 2
Impact on the Partnership's net income							3	3	7	7		3	4	7	7		2	1	3	1				1			1	1	2	2		1	1	2	2
Amounts payable to TransCanada and its affiliates							3		3		3	3		3		3	3		3		3	1		1		1					1					1
Percentage of capital and operating costs charged by TransCanada's subsidiaries									100.00%					100.00%					100.00%					100.00%
Ownership interest at the end of the period (as a percent)	25.00%	25.00%
Transportation revenues from TransCanada and its affiliates							17	18	41	42
Percentage of transportation revenues to total revenues							37.00%	28.00%	43.00%	32.00%
Revenue from TransCanada and its affiliates included in the Partnership's equity income from Great Lakes							8	9	19	20
Great Lakes' receivables for transportation contracts with TransCanada and its affiliates							$ 6		$ 6		$ 7