LONG-TERM INVESTMENTS - Narrative (Details) - CAD ($) shares in Millions, $ in Millions	1 Months Ended			12 Months Ended
	Aug. 31, 2020	Mar. 31, 2020	Jan. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Goodwill of investee				$ 1,800	$ 2,100
Amortizable assets of investee				657	681
Dividends received from equity investments				2,100	2,200	$ 2,800
Impairment of equity investments				2,351	0	0
Loss from equity method investment				$ (1,136)	(1,503)	$ (1,509)
Steckman Ridge, LP
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)				50.00%
Impairment of equity investments				$ 221
Equity investment				$ 90	222
Southeast Supply Header L.L.C.
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)				50.00%
Impairment of equity investments				$ 394
Equity investment				$ 84	484
DCP Midstream, LLC
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)				50.00%
Impairment of equity investments				$ 1,700
Equity investment				331	$ 2,200
Loss from equity method investment				$ 324
Common Shares | Noverco Common Shares
Schedule of Equity Method Investments [Line Items]
Reciprocal shareholding (as a percent)				0.20%	0.50%
Equity Method Investment, number of shares sold (in shares)	5.7	1.0	11.6
Indirect pro-rata interest (as a percent)				0.10%	0.20%
Reduction from reciprocal shareholding				$ 29	$ 51
Preference shares (Note 21) | Noverco Common Shares
Schedule of Equity Method Investments [Line Items]
Maturity period				10 years
Margin (as a percent)				4.38%
Gas Distribution and Storage | Common Shares | Noverco Common Shares
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)				38.90%	38.90%
Equity investment				$ 156	$ 95