SEGMENTED INFORMATION (Details) - CAD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segmented Information
Total operating revenues	$ 12,352	$ 11,598	$ 13,263	$ 12,856	$ 11,562	$ 11,345	$ 10,745	$ 12,726	$ 50,069	$ 46,378	$ 44,378
Commodity and gas distribution costs									(31,004)	(29,401)	(28,637)
Operating and administrative									(6,991)	(6,792)	(6,442)
Impairment of long-lived assets									(423)	(1,104)	(4,463)
Impairment of goodwill									0	(1,019)	(102)
Income/(loss) from equity investments									1,503	1,509	1,102
Other income/(expense)									435	(52)	452
Earnings/(loss) before interest, income tax expense, and depreciation and amortization									13,589	9,519	6,288
Depreciation and amortization									(3,391)	(3,246)	(3,163)
Interest expense									(2,663)	(2,703)	(2,556)
Income tax (expense) recovery									(1,708)	(237)	2,697
Earnings									5,827	3,333	3,266
Capital expenditures									5,550	6,872	8,422
Property, plant and equipment, net	93,723				94,540				93,723	94,540
Liquids Pipelines
Segmented Information
Impairment of goodwill										0
Gas Distribution and Storage
Segmented Information
Impairment of goodwill										0
Renewable Power Generation
Segmented Information
Impairment of goodwill										0
Business segments | Liquids Pipelines
Segmented Information
Total operating revenues									10,219	8,079	8,913
Commodity and gas distribution costs									(29)	(16)	(18)
Operating and administrative									(3,298)	(3,124)	(2,949)
Impairment of long-lived assets									(21)	(180)	0
Impairment of goodwill										0	0
Income/(loss) from equity investments									780	577	416
Other income/(expense)									30	(5)	33
Earnings/(loss) before interest, income tax expense, and depreciation and amortization									7,681	5,331	6,395
Capital expenditures									2,548	3,102	2,799
Property, plant and equipment, net	48,783				49,214				48,783	49,214
Business segments | Gas Transmission and Midstream
Segmented Information
Total operating revenues									5,207	6,571	7,067
Commodity and gas distribution costs									0	(1,481)	(2,834)
Operating and administrative									(2,232)	(2,102)	(1,756)
Impairment of long-lived assets									(105)	(914)	(4,463)
Impairment of goodwill										(1,019)	(102)
Income/(loss) from equity investments									682	930	653
Other income/(expense)									(181)	349	166
Earnings/(loss) before interest, income tax expense, and depreciation and amortization									3,371	2,334	(1,269)
Capital expenditures									1,753	2,644	4,016
Property, plant and equipment, net	25,268				25,601				25,268	25,601
Business segments | Gas Distribution and Storage
Segmented Information
Total operating revenues									5,179	5,470	4,992
Commodity and gas distribution costs									(2,354)	(2,748)	(2,689)
Operating and administrative									(1,149)	(1,111)	(960)
Impairment of long-lived assets									0	0	0
Impairment of goodwill										0	0
Income/(loss) from equity investments									4	11	23
Other income/(expense)									67	89	24
Earnings/(loss) before interest, income tax expense, and depreciation and amortization									1,747	1,711	1,390
Capital expenditures									1,100	1,066	1,177
Property, plant and equipment, net	15,622				15,148				15,622	15,148
Business segments | Renewable Power Generation
Segmented Information
Total operating revenues									567	567	534
Commodity and gas distribution costs									(2)	(7)	0
Operating and administrative									(189)	(157)	(163)
Impairment of long-lived assets									(297)	(4)	0
Impairment of goodwill										0	0
Income/(loss) from equity investments									31	(28)	6
Other income/(expense)									1	(2)	(5)
Earnings/(loss) before interest, income tax expense, and depreciation and amortization									111	369	372
Capital expenditures									23	33	321
Property, plant and equipment, net	3,658				4,335				3,658	4,335
Business segments | Energy Services
Segmented Information
Total operating revenues									29,374	26,228	23,282
Commodity and gas distribution costs									(29,091)	(25,689)	(23,508)
Operating and administrative									(44)	(73)	(47)
Impairment of long-lived assets									0	0	0
Impairment of goodwill										0	0
Income/(loss) from equity investments									8	18	8
Other income/(expense)									3	(2)	2
Earnings/(loss) before interest, income tax expense, and depreciation and amortization									250	482	(263)
Capital expenditures									2	0	1
Property, plant and equipment, net	24				22				24	22
Intersegment revenue
Segmented Information
Total operating revenues									(477)	(537)	(410)
Commodity and gas distribution costs									472	540	412
Operating and administrative									(79)	(225)	(567)
Impairment of long-lived assets									0	(6)	0
Impairment of goodwill										0	0
Income/(loss) from equity investments									(2)	1	(4)
Other income/(expense)									515	(481)	232
Earnings/(loss) before interest, income tax expense, and depreciation and amortization									429	(708)	(337)
Capital expenditures									124	27	$ 108
Property, plant and equipment, net	$ 368				$ 220				$ 368	$ 220
Customer Concentration Risk | Sales Revenue, Net | Largest Non-Affiliated Customer
Out of period adjustments
Concentration (percent)											11.80%