Post-Employment Benefits - Summary of Affected Defined Benefit Obligation Due to Reasonable Possible Changes to Principal Actuarial Assumptions (Detail) - Canada plan [member] $ in Millions	Oct. 31, 2025 CAD ($)
Pension plan [member] | Actuarial assumption of discount rates [member]
Disclosure of defined benefit plans [line items]
Decrease in assumption	$ 1,054
Increase in assumption	(889)
Pension plan [member] | Actuarial assumption of rate of compensation increase [member]
Disclosure of defined benefit plans [line items]
Decrease in assumption	(205)
Increase in assumption	217
Pension plan [member] | Actuarial assumption of future mortality [member]
Disclosure of defined benefit plans [line items]
1 year shorter life expectancy	(167)
1 year longer life expectancy	161
Other post employment benefit plans [member] | Actuarial assumption of discount rates [member]
Disclosure of defined benefit plans [line items]
Decrease in assumption	44
Increase in assumption	(37)
Other post employment benefit plans [member] | Actuarial assumption of health care cost trend rates [member]
Disclosure of defined benefit plans [line items]
Decrease in assumption	(13)
Increase in assumption	15
Other post employment benefit plans [member] | Actuarial assumption of future mortality [member]
Disclosure of defined benefit plans [line items]
1 year shorter life expectancy	(8)
1 year longer life expectancy	$ 8