Pensions and other benefits - Changes in Fund Assets (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Change in fund assets:
Fair value of fund assets at January 1	$ 14,365
Fair value of fund assets at December 31	14,938	$ 14,365
Pensions
Change in fund assets:
Fair value of fund assets at January 1	14,365	13,319
Actual return on fund assets	1,180	1,634
Employer contributions	18	27
Employee contributions	42	42
Benefits paid	(667)	(653)
Foreign currency changes	0	(4)
Fair value of fund assets at December 31	14,938	14,365
Funded status – plan surplus (deficit)	2,054	566
Other benefits
Change in fund assets:
Fair value of fund assets at January 1	5	5
Actual return on fund assets	0	0
Employer contributions	31	34
Employee contributions	0	0
Benefits paid	(31)	(34)
Foreign currency changes	0	0
Fair value of fund assets at December 31	5	5
Funded status – plan surplus (deficit)	$ (498)	$ (548)