Financial instruments - Financial Risk Management (Details) $ in Millions, $ in Millions	3 Months Ended			4 Months Ended		6 Months Ended	12 Months Ended
	Dec. 31, 2022 CAD ($)	Dec. 31, 2021 CAD ($)	Mar. 31, 2021 CAD ($)	Dec. 31, 2021 CAD ($)	Sep. 14, 2021 CAD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2022 CAD ($)	Dec. 31, 2021 CAD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 CAD ($)	May 21, 2021 CAD ($)	May 21, 2021 USD ($)
FX Forward Contracts
Schedule of Investments [Line Items]
Gain (loss) on derivative							$ 0	$ (13)
Derivative entered into, Notional amount									$ 1,000
Derivative notional amount	$ 0	$ 0		$ 0			0	0
Forward starting swaps
Schedule of Investments [Line Items]
Gain (loss) on derivative				(94)	$ 251
Derivative term						30 years
Derivative notional amount	1,745	2,967		2,967		$ 2,400	1,745	2,967				$ 2,400
Net deferred losses on derivatives and other		(21)		(21)				(21)			$ 73
Derivative, gain (loss), settlement		230
Bond locks
Schedule of Investments [Line Items]
Gain (loss) on derivative	$ (7)			(19)	$ 10
Derivative term			7 years
Derivative notional amount			$ 600								600
Net deferred losses on derivatives and other		$ (17)		$ (17)				(17)			$ 2
Treasury Rate Locks | Net Interest Expense
Schedule of Investments [Line Items]
Derivative losses amortized to net interest expense							6	10		$ 10
Net gains (losses) expected to be recognized in next 12 months							6
Net Investment Hedge
Schedule of Investments [Line Items]
Gain (loss) on derivative							$ 471	$ (25)		$ (136)