CREDIT FACILITIES, SHORT-TERM LOAN FACILITY AND LONG-TERM DEBT (Details) (USD $)	3 Months Ended	0 Months Ended			3 Months Ended	0 Months Ended
	Mar. 31, 2015	Apr. 01, 2015	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Mar. 13, 2015
Credit facilities, short-term loan facility and long-term debt
Credit facilities, short-term loan facility and long-term debt	$ 2,034,000,000		2,034,000,000	1,695,000,000
Less: current portion	249,000,000		249,000,000	249,000,000
Long-term debt	1,785,000,000		1,785,000,000	1,446,000,000
Net proceeds	349,000,000
3.82% Series D Senior Notes due 2017
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	3.82%		3.82%	3.82%
Credit facilities, short-term loan facility and long-term debt	20,000,000		20,000,000	20,000,000
Senior Credit Facility, Term Loan Facilities and Short-Term Loan Facility
Credit facilities, short-term loan facility and long-term debt
Leverage ratio (as a percent)		4.97%	5.20%
Senior Credit Facility, Term Loan Facilities and Short-Term Loan Facility | Debt agreement covenants, initial period after occurrence of acquisition
Credit facilities, short-term loan facility and long-term debt
Additional period immediately following the fiscal quarter in which a specified material acquisition occurs	6 months
Senior Credit Facility, Term Loan Facilities and Short-Term Loan Facility | Debt agreement covenants, initial period after occurrence of acquisition | Maximum
Credit facilities, short-term loan facility and long-term debt
Leverage ratio (as a percent)	5.50%
Senior Credit Facility, Term Loan Facilities and Short-Term Loan Facility | Debt agreement covenants, periods subsequent to initial period after occurrence of acquisition | Maximum
Credit facilities, short-term loan facility and long-term debt
Leverage ratio (as a percent)	5.00%
Term loan | Short-Term Loan Facility due 2015
Credit facilities, short-term loan facility and long-term debt
Credit facilities, short-term loan facility and long-term debt	170,000,000		170,000,000	170,000,000
Term loan | Short-Term Loan Facility due 2015 | LIBOR
Credit facilities, short-term loan facility and long-term debt
Variable rate basis	LIBOR
Debt average interest rate (as a percent)	1.30%
Debt interest rate, at period end (as a percent)	1.30%		1.30%
Senior revolving credit facility | Senior Credit Facility due 2017
Credit facilities, short-term loan facility and long-term debt
Credit facilities, short-term loan facility and long-term debt	320,000,000		320,000,000	330,000,000
Maximum borrowing capacity	500,000,000		500,000,000
Amount outstanding under credit facility	320,000,000		320,000,000	330,000,000
Remaining borrowing capacity	180,000,000		180,000,000
Senior revolving credit facility | Senior Credit Facility due 2017 | LIBOR
Credit facilities, short-term loan facility and long-term debt
Variable rate basis	LIBOR			LIBOR	LIBOR
Debt average interest rate (as a percent)	1.43%				1.42%
Debt interest rate, at period end (as a percent)	1.43%		1.43%	1.41%
Term loan | Term Loan Facility due 2018
Credit facilities, short-term loan facility and long-term debt
Credit facilities, short-term loan facility and long-term debt	500,000,000		500,000,000	500,000,000
Term loan | Term Loan Facility due 2018 | LIBOR borrowings | LIBOR
Credit facilities, short-term loan facility and long-term debt
Variable rate basis	LIBOR			LIBOR	LIBOR
Debt average interest rate (as a percent)	1.43%				1.42%
Debt interest rate, at period end (as a percent)	1.43%		1.43%	1.41%
Term loan | Term Loan Facility due 2018 | LIBOR borrowings | LIBOR | Hedges of cash flows | Interest rate swaps
Credit facilities, short-term loan facility and long-term debt
Debt average interest rate (as a percent)	1.83%				1.83%
Unsecured debt | 4.65% Senior Notes due 2021
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	4.65%		4.65%	4.65%
Discount	0		0	0
Credit facilities, short-term loan facility and long-term debt	350,000,000		350,000,000	350,000,000
Unsecured debt | 4.375% Senior Notes due 2025
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	4.375%		4.375%			4.375%
Discount	1,000,000		1,000,000
Credit facilities, short-term loan facility and long-term debt	349,000,000		349,000,000
Amount of debt						350,000,000
Net proceeds						346,000,000
Unsecured debt | 5.09% Senior Notes due 2015
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	5.09%		5.09%	5.09%
Credit facilities, short-term loan facility and long-term debt	75,000,000		75,000,000	75,000,000
Unsecured debt | 5.29% Senior Notes due 2020
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	5.29%		5.29%	5.29%
Credit facilities, short-term loan facility and long-term debt	100,000,000		100,000,000	100,000,000
Unsecured debt | 5.69% Senior Notes due 2035
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	5.69%		5.69%	5.69%
Credit facilities, short-term loan facility and long-term debt	$ 150,000,000		150,000,000	150,000,000
Subsequent event | GTN | Former parent, TransCanada subsidiaries | Transaction between entities under common control
Credit facilities, short-term loan facility and long-term debt
Interest acquired by Partnership (as a percent)		30.00%
GTN | Unsecured debt | 5.09% Senior Notes due 2015
Credit facilities, short-term loan facility and long-term debt
Stated interest rate (as a percent)	5.09%		5.09%
GTN | Senior Notes | Maximum
Credit facilities, short-term loan facility and long-term debt
Percentage of debt to total capitalization	70.00%