Leases Supplemental Information Related to Leases (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 CAD ($)
Leases [Abstract]
Operating cash outflows from operating leases	$ 82
Operating cash outflows from finance leases	10
Financing cash outflows from finance leases	6
Right-of-use assets obtained in exchange for operating lease liabilities	38
Right-of-use assets obtained in exchange for finance lease liabilities	$ 4