Major Commitments and Contingencies (Purchase Commitments) (Details) CAD in Millions	12 Months Ended
Dec. 31, 2017 CAD
Other Commitments [Member]
Long-term Purchase Commitment [Line Items]
Aggregate commitment costs	CAD 2,170

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
Period Type:	duration