Pensions and Other Benefits - Pension Plan Asset (Detail) - CAD CAD in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of fund assets at December 31	CAD 12,808	CAD 12,196
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation at December 31	(11,679)	(11,399)	CAD (11,194)
Fair value of fund assets at December 31	12,808	12,196	CAD 12,300
Funded Status	1,129	797
Pension plans in surplus [Member] \| Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation at December 31	(11,174)	(10,902)
Fair value of fund assets at December 31	12,581	11,972
Funded Status	1,407	1,070
Pension plans in deficit [Member] \| Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation at December 31	(505)	(497)
Fair value of fund assets at December 31	227	224
Funded Status	CAD (278)	CAD (273)

Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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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.

+ References

No definition available.

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Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

+ References

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- Definition

Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64852052&loc=d3e1703-114919

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