Pensions and Other Postretirement Benefits (Defined Contribution and Other Plans) (Details) - CAD CAD in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pensions [Member]
Defined contribution and other plans disclosure [Line Items]
Employer's contributions	CAD 19	CAD 18	CAD 18

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.

No definition available.

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Balance Type:	na
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