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Preferred Shares - Characteristics Specific to Series of Preferred Shares (Details) - CAD / shares | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Disclosure of classes of share capital [line items] |  |  |
Annual dividend rate per share |  | CAD 0.16 | CAD 0.72
Series A |  |  |
Disclosure of classes of share capital [line items] |  |  |
Annual dividend rate per share | CAD 0.67725 |  |
Series A | Benchmark |  |  |
Disclosure of classes of share capital [line items] |  |  |
Rate spread over Benchmark | 2.03% |  |
Series B |  |  |
Disclosure of classes of share capital [line items] |  |  |
Annual dividend rate per share | CAD 0.7255 |  |
Series B | Benchmark |  |  |
Disclosure of classes of share capital [line items] |  |  |
Rate spread over Benchmark | 2.03% |  |
Series C |  |  |
Disclosure of classes of share capital [line items] |  |  |
Annual dividend rate per share | CAD 1.00675 |  |
Series C | Benchmark |  |  |
Disclosure of classes of share capital [line items] |  |  |
Rate spread over Benchmark | 3.10% |  |
Series D |  |  |
Disclosure of classes of share capital [line items] |  |  |
Annual dividend rate per share | CAD 0.0000 |  |
Series D | Benchmark |  |  |
Disclosure of classes of share capital [line items] |  |  |
Rate spread over Benchmark | 3.10% |  |
Series E |  |  |
Disclosure of classes of share capital [line items] |  |  |
Annual dividend rate per share | CAD 1.29850 |  |
Series E | Benchmark |  |  |
Disclosure of classes of share capital [line items] |  |  |
Rate spread over Benchmark | 3.65% |  |
Series F |  |  |
Disclosure of classes of share capital [line items] |  |  |
Annual dividend rate per share | CAD 0.0000 |  |
Series F | Benchmark |  |  |
Disclosure of classes of share capital [line items] |  |  |
Rate spread over Benchmark | 3.65% |  |
Series G |  |  |
Disclosure of classes of share capital [line items] |  |  |
Annual dividend rate per share | CAD 1.325 |  |
Series G | Benchmark |  |  |
Disclosure of classes of share capital [line items] |  |  |
Rate spread over Benchmark | 3.80% |  |
Series H |  |  |
Disclosure of classes of share capital [line items] |  |  |
Annual dividend rate per share | CAD 0.0000 |  |
Series H | Benchmark |  |  |
Disclosure of classes of share capital [line items] |  |  |
Rate spread over Benchmark | 3.80% |  |

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