PARTNERS' EQUITY (Details) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended		0 Months Ended		0 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended			0 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Jul. 22, 2013 Bison Former parent, TransCanada Subsidiaries	May 03, 2011 Bison Former parent, TransCanada Subsidiaries	May 22, 2013 Common Units	Sep. 30, 2013 Common Units	May 22, 2013 General Partner	Sep. 30, 2013 General Partner	Sep. 30, 2013 Limited Partners	Dec. 31, 2012 Limited Partners	May 22, 2013 General Partner	Sep. 30, 2013 General Partner	Dec. 31, 2012 General Partner	Sep. 30, 2013 TransCanada Corporation
Public offering
Units sold in public offering					8,855,000	8,800,000
Units sold in public offering pursuant to exercise of underwriters' option					1,155,000
Price per common unit in public offering					$ 43.85
Gross proceeds from public offering of common units					$ 388
Net proceeds from public offering of common units					373	373
Partners' Equity
General partner ownership interest in the partnership (as a percent)											2.00%	2.00%
Capital contribution							8	8
Aggregate ownership interest in the Partnership (as a percent)									98.00%			11.10%	12.60%
Number of common units owned	62,300,000	53,500,000							62,327,766	53,472,766		5,797,106		11,287,725
Amount received from TransCanada subsidiary as a post-closing construction expenditures adjustment	$ 1		$ 1
Interest acquired by the Partnership (as a percent)				25.00%