PARTNERS' EQUITY (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended				12 Months Ended		1 Months Ended	12 Months Ended
	May 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Limited Partners	Dec. 31, 2011 Limited Partners	May 31, 2011 General Partner	Dec. 31, 2012 General Partner	Dec. 31, 2011 General Partner	Dec. 31, 2012 TransCanada Corporation
Public offering
Number of common units sold in public offering	7,245,000
Price per common unit in public offering	$ 47.58
Gross proceeds from public offering of common units	$ 345
Net proceeds from public offering of common units	331
Common units and interest in the partnership
Capital contribution by general partner							$ 7
Aggregate ownership interest in the Partnership (as a percent)					98.00%			12.60%	12.60%	33.30%
Number of common units owned		53,500,000	53,500,000	46,200,000	53,472,766	53,472,766		5,797,106		11,287,725
General partner ownership interest in the partnership (as a percent)								2.00%