Pensions and Other Benefits - Summary of Defined Benefit Pension Plan Assets Measured at Fair Value Using Unobservable Inputs (Detail) - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of fund assets, Beginning	$ 12,808
Fair value of fund assets, Ending	12,349	$ 12,808
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of fund assets, Beginning	12,808	12,196
Net realized gains	82	1,183
Fair value of fund assets, Ending	12,349	12,808
Real estate
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of fund assets, Beginning	622
Fair value of fund assets, Ending	697	622
Fair Value, Inputs, Level 3 [Member] \| Real estate \| Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of fund assets, Beginning	$ 0	437
Disbursements		(43)
Net realized gains		7
Decrease in net unrealized gains		(7)
Net transfers (out of) Level 3		(394)
Fair value of fund assets, Ending		$ 0

Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets sold.

+ References

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

+ References

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

+ References

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-Publisher FASB
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- Definition

Amount of transfers of financial instrument classified as a liability out of level 3 of the fair value hierarchy.

+ References

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