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Summary of Significant Accounting Policies - Employee Future Benefits and Stock-Based Compensation (Details) - CAD / shares | 12 Months Ended |
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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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- Definition 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 + Details
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