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Summary of Significant Accounting Policies - Employee Future Benefits and Stock-Based Compensation (Details) - CAD / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Defined benefit plan, market-related value of plan assets recognition period	3 years
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
DSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price, VWAP (period)	5 days
Volume weighted average price, share price (in dollars per share)		CAD 37.72
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Exercise price, VWAP (period)	5 days
Volume weighted average price, share price (in dollars per share)	CAD 41.46	37.72
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Exercise price, VWAP (period)	5 days
Volume weighted average price, share price (in dollars per share)	CAD 41.46	CAD 37.72

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Defined Benefit Plan, Market-Related Value of Plan Assets, Recognition Period

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Share-Based Compensation Arrangement By Share-Based Payment Award, Fair Value Assumptions, Volume Weighted Average Price, Share Price

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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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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