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Maximum value of underlying asset represented by financial derivatives, excluding currency forwards.

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Percentage Of Defined Benefit Plan Exposed To Foreign Currency Risk, Excluding Currency Forwards

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

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Amount of employer security in which defined benefit plan asset is invested. Includes, but is not limited to, security issued or managed by related party of employer.

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Amount of decrease in accumulated postretirement benefit obligation from one-percentage-point decrease in assumed health care cost trend rate.

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Number of shares of employer stock in which defined benefit plan asset is invested. Includes, but is not limited to, stock issued or managed by related party of employer.

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Amount of cost for defined contribution plan.

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Pensions and Other Benefits - Additional Information (Detail) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Period of average market values for calculating net periodic benefit cost	5 years
Effect of one percentage point increase on the total of service and interest costs	$ 0
Effect of one percentage point decrease on the total of service and interest costs	0
Effect of one percentage point increase on post-retirement benefit obligation	(5)
Effect of one percentage point decrease on post-retirement benefit obligation	$ 5
Maximum value of underlying assets represented by financial derivatives, excluding currency forwards	30.00%
Company's common shares in fund assets, Shares	86,084	107,330
Net cost of defined contribution plan	$ 10	$ 9	$ 9
Multi-employer plan contributions	3	5	$ 4
Equity Securities [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Company's securities in fund assets	21	25
Debt Securities [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Company's securities in fund assets	$ 1	1
US Dollar [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Plans exposure to foreign currency risk percentage	33.00%
Percentage of plan exposed to foreign currency risk, excluding currency forwards	43.00%
European Currencies [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Plans exposure to foreign currency risk percentage	4.00%
Other Currency [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Plans exposure to foreign currency risk percentage	13.00%
Pension Plans, Defined Benefit [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Defined benefit pension plans' accumulated benefit obligation	$ 10,981	$ 11,273
Unamortized actuarial loss expected to be recognized in next fiscal year	82
Unamortized prior service cost expected to be recognized in next fiscal year	1
Other Post-retirement Benefit Plans, Defined Benefit [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Unamortized actuarial loss expected to be recognized in next fiscal year	2
Unamortized prior service cost expected to be recognized in next fiscal year	$ 1