QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - CAD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
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
Operating income	1,768	1,588	2,285	2,619	1,513	854	1,571	878	8,260	4,816	1,571
Earnings	914	1,060	1,830	2,023	1,283	213	1,327	510	5,827	3,333	3,266
Earnings attributable to controlling interests	842	1,045	1,832	1,986	1,184	4	1,160	534	5,705	2,882	2,859
Earnings/(loss) attributable to common shareholders	$ 746	$ 949	$ 1,736	$ 1,891	$ 1,089	$ (90)	$ 1,071	$ 445	$ 5,322	$ 2,515	$ 2,529
Earnings per common share
Earnings per common share attributable to common shareholders (in CAD per share)	$ 0.37	$ 0.47	$ 0.86	$ 0.94	$ 0.60	$ (0.05)	$ 0.63	$ 0.26	$ 2.64	$ 1.46	$ 1.66
Diluted earnings per common share attributable to common shareholders (in CAD per share)	$ 0.36	$ 0.47	$ 0.86	$ 0.94	$ 0.60	$ (0.05)	$ 0.63	$ 0.26	$ 2.63	$ 1.46	$ 1.65