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Business acquisitions and development projects - Acquisition of Empire (Details) - CAD CAD in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Business Acquisition [Line Items] |  |  |
Goodwill (note 6) | CAD 1,196,234 | CAD 306,641 | CAD 110,493
Business Acquisition, Pro Forma Information [Abstract] |  |  |
Revenues | 1,977,809 | 1,908,340 |
Net earnings attributable to common shareholders | 229,976 | CAD 213,983 |
Empire |  |  |
Business Acquisition [Line Items] |  |  |
Working capital | 55,441 |  |
Property, plant and equipment | 2,764,441 |  |
Goodwill (note 6) | 1,010,273 |  |
Regulatory assets | 318,130 |  |
Other assets | 58,553 |  |
Long-term debt | (1,218,563) |  |
Regulatory liabilities | (195,489) |  |
Pension and OPEB | (105,005) |  |
Deferred income tax liability, net | (562,397) |  |
Other liabilities | (102,759) |  |
Total net assets acquired | 2,022,625 |  |
Cash and cash equivalent | 2,338 |  |
Net assets acquired, net of cash and cash equivalent | CAD 2,020,287 |  |

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