Other Long-Term Obligations (Parenthetical) (Detail) - CAD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Schedule of Other Liabilities [Line Items]
Employee retirement benefit obligations in current liabilities	$ 58	$ 58
Asset retirement obligations and other environmental liabilities in current liabilities	124	124
Undiscounted Commitments	27	6
Accounts Payable and Accrued Liabilities [Member]
Schedule of Other Liabilities [Line Items]
Lease liability due within one year, Operating leases	$ 106	$ 115