Accumulated Other Comprehensive Income (Loss) - Accumulated Other Comprehensive Income (Details) - CAD ($) $ in Thousands	6 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	$ 3,594,297	$ 3,486,520
Settlement of unsecured senior notes	235,758
Ending balance	1,628,129	4,245,620
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(57,468)	(28,246)
Other comprehensive (loss) income	9,773	(3,288)
Ending balance	(47,695)	(31,534)
Changes of Own Credit Risk of Financial Liabilities
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	15,186	(5,994)
Settlement of unsecured senior notes	(29,507)
Other comprehensive (loss) income	28,309	10,080
Ending balance	13,988	4,086
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(42,282)	(34,240)
Settlement of unsecured senior notes	(29,507)
Other comprehensive (loss) income	38,082	6,792
Ending balance	$ (33,707)	$ (27,448)