QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - CAD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 10,008	$ 9,110	$ 7,956	$ 12,013	$ 12,352	$ 11,598	$ 13,263	$ 12,856	$ 39,087	$ 50,069	$ 46,378
Operating income	2,251	2,095	2,098	1,513	1,768	1,588	2,285	2,619	7,957	8,260	4,816
Earnings/(loss)	1,899	1,104	1,777	(1,364)	914	1,060	1,830	2,023	3,416	5,827	3,333
Earnings attributable to controlling interests	1,871	1,084	1,741	(1,333)	842	1,045	1,832	1,986	3,363	5,705	2,882
Earnings/(loss) attributable to common shareholders	$ 1,775	$ 990	$ 1,647	$ (1,429)	$ 746	$ 949	$ 1,736	$ 1,891	$ 2,983	$ 5,322	$ 2,515
Earnings/(loss) per common share
Earnings/(loss) per common share attributable to common shareholders (in CAD per share)	$ 0.88	$ 0.49	$ 0.82	$ (0.71)	$ 0.37	$ 0.47	$ 0.86	$ 0.94	$ 1.48	$ 2.64	$ 1.46
Diluted earnings/(loss) per common share attributable to common shareholders (in CAD per share)	$ 0.88	$ 0.49	$ 0.82	$ (0.71)	$ 0.36	$ 0.47	$ 0.86	$ 0.94	$ 1.48	$ 2.63	$ 1.46