Selected quarterly data (unaudited) (Details) $ / shares in Units, $ in Millions		3 Months Ended								12 Months Ended
	Apr. 21, 2021	Dec. 31, 2021 CAD ($) $ / shares	Sep. 30, 2021 CAD ($) $ / shares	Jun. 30, 2021 CAD ($) $ / shares	Mar. 31, 2021 CAD ($) $ / shares	Dec. 31, 2020 CAD ($) $ / shares	Sep. 30, 2020 CAD ($) $ / shares	Jun. 30, 2020 CAD ($) $ / shares	Mar. 31, 2020 CAD ($) $ / shares	Dec. 31, 2021 CAD ($) $ / shares	Dec. 31, 2020 CAD ($) $ / shares	Dec. 31, 2019 CAD ($) $ / shares
Quarterly Financial Information Disclosure [Abstract]
Stock split ratio	5
Total revenues		$ 2,040	$ 1,942	$ 2,054	$ 1,959	$ 2,012	$ 1,863	$ 1,792	$ 2,043	$ 7,995	$ 7,710	$ 7,792
Operating income		832	774	820	780	928	779	770	834	3,206	3,311	3,124
Net income		$ 532	$ 472	$ 1,246	$ 602	$ 802	$ 598	$ 635	$ 409	$ 2,852	$ 2,444	$ 2,440
Basic earnings per share (cad per share) | $ / shares		$ 0.74	$ 0.71	$ 1.87	$ 0.90	$ 1.19	$ 0.88	$ 0.94	$ 0.60	$ 4.20	$ 3.61	$ 3.52
Diluted earnings per share (cad per share) | $ / shares		$ 0.74	$ 0.70	$ 1.86	$ 0.90	$ 1.19	$ 0.88	$ 0.93	$ 0.60	$ 4.18	$ 3.59	$ 3.50