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Pension and other post-retirement benefits - Fair Value of Investments by Asset Category (Details) CAD in Thousands | Dec. 31, 2017 CAD
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Equity securities |
Defined Benefit Plan Disclosure [Line Items] |
Allocation percentage | 72.00%
Equity securities | Level 1 |
Defined Benefit Plan Disclosure [Line Items] |
Fair value of plan assets | CAD 505,219
Debt securities |
Defined Benefit Plan Disclosure [Line Items] |
Allocation percentage | 27.00%
Debt securities | Level 1 |
Defined Benefit Plan Disclosure [Line Items] |
Fair value of plan assets | CAD 164,281
Other |
Defined Benefit Plan Disclosure [Line Items] |
Allocation percentage | 0.00%
Other | Level 1 |
Defined Benefit Plan Disclosure [Line Items] |
Fair value of plan assets | CAD 945

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