Shareholders' Equity - Narrative (Details) - CAD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Dec. 17, 2019	Oct. 19, 2018
Common Shares repurchased	100,000	900,000		1,700,000	1,600,000
Common Shares repurchased (value)	$ 52	$ 296		$ 520	$ 481
Current Normal Course Issuer Bid (NCIB)
Common Shares authorized to be repurchased						4,800,000
Common Shares repurchased	150,860		1,900,000	1,606,714
Common Shares repurchased (value)	$ 52		$ 620	$ 520
2018 Normal Course Issuer Bid (NCIB)
Common Shares authorized to be repurchased							5,680,000
Common Shares repurchased		956,243			1,663,921
Common Shares repurchased (value)		$ 296			$ 481