Change in Plan Assets and Plan Assets in Excess of Less Than Projected Benefit Obligation (Detail) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Schedule Of Defined Benefit Plans Disclosures [Line Items]
Fair value at January 1	$ 9,426
Fair value at December 31	9,440	$ 9,426
Pension benefits
Schedule Of Defined Benefit Plans Disclosures [Line Items]
Fair value at January 1	9,426	8,599
Actual return on plan assets	319	1,073
Company contributions	164	195
Benefits paid	(469)	(441)
Fair value at December 31	9,440	9,426
Funded plans	89	(641)
Unfunded plans	(499)	(649)
Total	(410)	(1,290)
Other postretirement benefits
Schedule Of Defined Benefit Plans Disclosures [Line Items]
Unfunded plans	(818)	(873)
Total	$ (818)	$ (873)