Common Share Activities (Detail) - CAD ($) shares in Thousands, $ in Millions		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Class of Stock [Line Items]
Common stock beginning balance, shares				743,902
Common stock, ending balance, shares		734,077		734,077		743,902
Common stock beginning balance, value	[1]			$ 1,375
Common stock, ending balance, value	[1]	$ 1,357		$ 1,357		$ 1,375
Common Stock
Class of Stock [Line Items]
Common stock beginning balance, shares				743,902	782,565	782,565
Issued under employee share-based awards, shares				0		1
Purchases at stated value, shares				(9,825)		(38,664)
Common stock, ending balance, shares		734,077		734,077		743,902
Common stock beginning balance, value				$ 1,375	$ 1,446	$ 1,446
Issued under employee share-based awards, value				0		0
Purchases at stated value, value		$ 0	$ (17)	(18)	$ (36)	(71)
Common stock, ending balance, value		$ 1,357		$ 1,357		$ 1,375

[1] Number of common shares authorized and outstanding were 1,100 million and 734 million, respectively (2019 - 1,100 million and 744 million, respectively).