Shareholders' Equity - Narrative (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2020	Mar. 31, 2019	Dec. 17, 2019	Oct. 19, 2018
Common Shares repurchased		1,600,000	700,000
Common Shares repurchased (value)		$ 468	$ 185
Current Normal Course Issuer Bid (NCIB)
Common Shares authorized to be repurchased				4,800,000
Common Shares repurchased	1,750,000	1,455,854
Common Shares repurchased (value)	$ 568	$ 468
2018 Normal Course Issuer Bid (NCIB)
Common Shares authorized to be repurchased					5,680,000
Common Shares repurchased			707,678
Common Shares repurchased (value)			$ 185