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Estimated 2020 Amortization from Accumulated Other Comprehensive Income (Detail)
$ in Millions
Dec. 31, 2019
CAD ($)
Pension benefits  
Defined Benefit Plan Disclosure [Line Items]  
Net actuarial loss (gain) $ 157 [1]
Prior service cost 13 [2]
Other postretirement benefits  
Defined Benefit Plan Disclosure [Line Items]  
Net actuarial loss (gain) $ 9 [1]
[1] The company amortizes the net balance of actuarial loss (gain) as a component of net periodic benefit cost over the average remaining service period of active plan participants.
[2] The company amortizes prior service cost on a straight-line basis.