PARTNERS' EQUITY (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended			9 Months Ended		1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended
	May 31, 2011	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 Limited Partners	Dec. 31, 2010 Limited Partners	May 31, 2011 General Partner	Sep. 30, 2011 General Partner	Sep. 30, 2011 General Partner	Dec. 31, 2010 General Partner	Sep. 30, 2011 TransCanada Corporation
Public offering
Number of common units sold in public offering	7,245,000
Price per common unit in public offering (in dollars per unit)	$ 47.58
Gross proceeds from public offering of common units	$ 344.7
Net proceeds from public offering of common units	330.9
Common units and interest in the partnership
Capital contribution by general partner						$ 6.7
Aggregate ownership interest in the Partnership (as a percent)				98.00%				12.60%	14.30%	33.30%
Number of common units owned		53,500,000	46,200,000	53,472,766	46,227,766		5,797,106	5,797,106		11,287,725
General partner ownership interest in the partnership (as a percent)						2.00%	2.00%	2.00%