Other Long-Term Liabilities - Narrative (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Liabilities Disclosure [Abstract]
Expected time period for payment of provision for environmental remediation	10
Environmental remediation costs charged to income	$ 10	$ 6	$ 6