RELATED PARTY TRANSACTIONS (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
General Partner
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates	$ 0.6	$ 0.5	$ 1.2	$ 1.0
North Baja Pipeline, LLC | TransCanada Corporation
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates	0.9	0.7	1.8	1.4
Impact on the Partnership's net income	0.9	0.7	1.6	1.4
Amounts payable to TransCanada and its affiliates	0.4		0.4		0.6
GTN | TransCanada Corporation
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates	5.8		5.8
Impact on the Partnership's net income	5.5		5.5
Amounts payable to TransCanada and its affiliates	0.4		0.4
Bison | TransCanada Corporation
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates	2.0		2.0
Impact on the Partnership's net income	0.8		0.8
Amounts payable to TransCanada and its affiliates	1.2		1.2
TransCanada Corporation | Great Lakes
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates	7.2	8.2	15.0	15.8
Impact on the Partnership's net income	3.3	3.5	6.8	6.9
Amounts payable to TransCanada and its affiliates	2.9		2.9		3.0
TransCanada and its affiliates contracts' remaining term, low end of range (in years)			1
TransCanada and its affiliates contracts' remaining term, high end of range (in years)			7
Transportation revenues from TransCanada and its affiliates	17.8	40.4	42.2	80.4
Percentage of transportation revenues to total revenues (as a percent)	28.00%	64.20%	31.60%	59.20%
Affiliated rental revenue	0.3	0.2	0.6	0.3
Revenue from TransCanada and its affiliates included in the Partnership's equity income from Great Lakes	8.4	18.8	19.9	37.4
Great Lakes' receivables for transportation contracts with TransCanada and its affiliates	7.1		7.1		11.0
TransCanada Corporation | Northern Border
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates	7.5	7.7	14.2	14.6
Impact on the Partnership's net income	3.4	3.4	6.6	6.6
Amounts payable to TransCanada and its affiliates	2.6		2.6		2.2
TransCanada Corporation | Tuscarora Gas Transmission Company
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates	1.1	0.9	2.0	1.9
Impact on the Partnership's net income	1.1	0.9	2.0	1.8
Amounts payable to TransCanada and its affiliates	$ 0.6		$ 0.6		$ 0.7