RELATED PARTY TRANSACTIONS (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
General Partner
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates	$ 1	$ 1
TransCanada Corporation | Great Lakes
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates	8	8
Impact on the Partnership's net income	4	4
Amounts payable to TransCanada and its affiliates	3		4
Percentage of capital and operating costs charged by TransCanada's subsidiaries	100.00%
Transportation revenues from TransCanada and its affiliates	21	24
Percentage of transportation revenues to total revenues	59.00%	48.00%
Revenue from TransCanada and its affiliates included in the Partnership's equity earnings from Great Lakes	10	11
Great Lakes' receivables for transportation contracts with TransCanada and its affiliates	8		10
TransCanada Corporation | Northern Border
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates	7	8
Impact on the Partnership's net income	3	4
Amounts payable to TransCanada and its affiliates	3		4
Percentage of capital and operating costs charged by TransCanada's subsidiaries	100.00%
TransCanada Corporation | GTN
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates	7	7
Impact on the Partnership's net income	2	2
Amounts payable to TransCanada and its affiliates	2		3
Percentage of capital and operating costs charged by TransCanada's subsidiaries	100.00%
TransCanada Corporation | Bison
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates	1	2
Impact on the Partnership's net income		1
Amounts payable to TransCanada and its affiliates			1
Percentage of capital and operating costs charged by TransCanada's subsidiaries	100.00%
TransCanada Corporation | North Baja
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates	1	1
Impact on the Partnership's net income	1	1
Amounts payable to TransCanada and its affiliates			1
TransCanada Corporation | Tuscarora
Costs charged to the pipeline system and amounts payable
Costs charged by TransCanada and its affiliates	1	1
Impact on the Partnership's net income	1	1
Amounts payable to TransCanada and its affiliates			$ 1