SEGMENTED INFORMATION (Details) - CAD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segmented Information
Revenues	$ 10,008	$ 9,110	$ 7,956	$ 12,013	$ 12,352	$ 11,598	$ 13,263	$ 12,856	$ 39,087	$ 50,069	$ 46,378
Commodity and gas distribution costs									(20,669)	(31,004)	(29,401)
Operating and administrative									(6,749)	(6,991)	(6,792)
Impairment of long-lived assets										(423)	(1,104)
Impairment of goodwill									0	0	(1,019)
Income/(loss) from equity investments									1,136	1,503	1,509
Impairment of equity investments									(2,351)	0	0
Other income/(expense)									238	435	(52)
Earnings before interest, income tax expense, and depreciation and amortization									10,692	13,589	9,519
Depreciation and amortization									(3,712)	(3,391)	(3,246)
Interest expense									(2,790)	(2,663)	(2,703)
Income tax (expense) recovery									(774)	(1,708)	(237)
Earnings									3,416	5,827	3,333
Capital expenditures									5,470	5,550	6,872
Property, plant and equipment, net (Note 11)	94,571				93,723				94,571	93,723	94,540
Business segments | Liquids Pipelines
Segmented Information
Revenues									10,423	10,219	8,079
Commodity and gas distribution costs									(20)	(29)	(16)
Operating and administrative									(3,331)	(3,298)	(3,124)
Impairment of long-lived assets										(21)	(180)
Impairment of goodwill											0
Income/(loss) from equity investments									558	780	577
Impairment of equity investments									0
Other income/(expense)									53	30	(5)
Earnings before interest, income tax expense, and depreciation and amortization									7,683	7,681	5,331
Capital expenditures									2,033	2,548	3,102
Property, plant and equipment, net (Note 11)	48,799				48,783				48,799	48,783	49,214
Business segments | Gas Transmission and Midstream
Segmented Information
Revenues									4,870	5,207	6,571
Commodity and gas distribution costs									0	0	(1,481)
Operating and administrative									(1,859)	(2,232)	(2,102)
Impairment of long-lived assets										(105)	(914)
Impairment of goodwill											(1,019)
Income/(loss) from equity investments									479	682	930
Impairment of equity investments									(2,351)
Other income/(expense)									(52)	(181)	349
Earnings before interest, income tax expense, and depreciation and amortization									1,087	3,371	2,334
Capital expenditures									2,130	1,753	2,644
Property, plant and equipment, net (Note 11)	25,745				25,268				25,745	25,268	25,601
Business segments | Gas Distribution and Storage
Segmented Information
Revenues									4,569	5,179	5,470
Commodity and gas distribution costs									(1,810)	(2,354)	(2,748)
Operating and administrative									(1,091)	(1,149)	(1,111)
Impairment of long-lived assets										0	0
Impairment of goodwill											0
Income/(loss) from equity investments									9	4	11
Impairment of equity investments									0
Other income/(expense)									71	67	89
Earnings before interest, income tax expense, and depreciation and amortization									1,748	1,747	1,711
Capital expenditures									1,134	1,100	1,066
Property, plant and equipment, net (Note 11)	16,079				15,622				16,079	15,622	15,148
Business segments | Renewable Power Generation
Segmented Information
Revenues									587	567	567
Commodity and gas distribution costs									(2)	(2)	(7)
Operating and administrative									(191)	(189)	(157)
Impairment of long-lived assets										(297)	(4)
Impairment of goodwill											0
Income/(loss) from equity investments									94	31	(28)
Impairment of equity investments									0
Other income/(expense)									35	1	(2)
Earnings before interest, income tax expense, and depreciation and amortization									523	111	369
Capital expenditures									81	23	33
Property, plant and equipment, net (Note 11)	3,495				3,658				3,495	3,658	4,335
Business segments | Energy Services
Segmented Information
Revenues									19,283	29,374	26,228
Commodity and gas distribution costs									(19,450)	(29,091)	(25,689)
Operating and administrative									(67)	(44)	(73)
Impairment of long-lived assets										0	0
Impairment of goodwill											0
Income/(loss) from equity investments									(3)	8	18
Impairment of equity investments									0
Other income/(expense)									1	3	(2)
Earnings before interest, income tax expense, and depreciation and amortization									(236)	250	482
Capital expenditures									2	2	0
Property, plant and equipment, net (Note 11)	24				24				24	24	22
Eliminations and Other
Segmented Information
Revenues									(645)	(477)	(537)
Commodity and gas distribution costs									613	472	540
Operating and administrative									(210)	(79)	(225)
Impairment of long-lived assets										0	(6)
Impairment of goodwill											0
Income/(loss) from equity investments									(1)	(2)	1
Impairment of equity investments									0
Other income/(expense)									130	515	(481)
Earnings before interest, income tax expense, and depreciation and amortization									(113)	429	(708)
Capital expenditures									90	124	27
Property, plant and equipment, net (Note 11)	$ 429				$ 368				$ 429	$ 368	$ 220
Customer Concentration Risk | Sales Revenue, Net | Largest Non-Affiliated Customer
Narrative
Concentration (percent)									13.60%