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Cumulative Preferred Stock (Narrative) (Details) - CAD CAD / shares in Units, CAD in Millions |  | 12 Months Ended
--- | --- | ---
Aug. 17, 2015 | Dec. 31, 2016 | Dec. 31, 2015
Class of Stock [Line Items] |  |  |
Net Proceeds from Issuance of Redeemable Preferred Stock |  | CAD 709 | CAD 709
Number of shares issued and outstanding |  | 29,000,000 | 29,000,000
Series A Preferred Stock [Member] |  |  |
Class of Stock [Line Items] |  |  |
Number of redeemable preferred shares issued | 6,000,000 | 3,864,636 |
Conversion of Stock, Shares Converted | 2,135,364 |  |
Number of shares issued and outstanding | 6,000,000 | 3,864,636 |
Annual Dividend Per Share |  | CAD 0.6388 |
Amount per share used to determine dividend per share |  | CAD 25 |
Term of Canada government bond yield |  | 5 years |
Series A Preferred Stock [Member] | Up To And Excluding August 15, 2020 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Annual Dividend Per Share |  | CAD 0.6388 |
Percentage rate used to determine dividend rate |  | 1.84% |
Outstanding share redemption price per share |  | CAD 25 |
Series A Preferred Stock [Member] | Up To And Excluding August 15, 2018 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Annual Dividend Per Share |  | CAD 1.025 |
Percentage rate used to determine dividend rate |  | 2.65% |
Outstanding share redemption price per share |  | CAD 25 |
Series A Preferred Stock [Member] | Up To And Excluding February 15, 2020 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Annual Dividend Per Share |  | CAD 1.0625 |
Percentage rate used to determine dividend rate |  | 2.63% |
Outstanding share redemption price per share |  | CAD 25 |
Series B Preferred Stock [Member] |  |  |
Class of Stock [Line Items] |  |  |
Number of redeemable preferred shares issued |  | 2,135,364 |
Number of shares issued and outstanding |  | 2,135,364 |
Annual Dividend Per Share |  | CAD 0.5724 |
Amount per share used to determine dividend per share |  | CAD 25 |
Percentage rate used to determine dividend rate |  | 1.84% |
Series B Preferred Stock [Member] | August 15, 2020 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | CAD 25 |
Series B Preferred Stock [Member] | August 15, 2023 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25 |
Series B Preferred Stock [Member] | February 15, 2025 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25 |
Series B Preferred Stock [Member] | After August 15, 2015 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25.5 |
Series B Preferred Stock [Member] | After August 15, 2018 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25.5 |
Series B Preferred Stock [Member] | After February 15, 2020 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25.5 |
Series C Preferred Stock [Member] |  |  |
Class of Stock [Line Items] |  |  |
Amount per share used to determine dividend per share |  | CAD 25 |
Term of Canada government bond yield |  | 5 years |
Series C Preferred Stock [Member] | Up To And Excluding August 15, 2020 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Annual Dividend Per Share |  | CAD 0.6388 |
Percentage rate used to determine dividend rate |  | 1.84% |
Outstanding share redemption price per share |  | CAD 25 |
Series C Preferred Stock [Member] | Up To And Excluding August 15, 2018 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Annual Dividend Per Share |  | CAD 1.025 |
Percentage rate used to determine dividend rate |  | 2.65% |
Outstanding share redemption price per share |  | CAD 25 |
Series C Preferred Stock [Member] | Up To And Excluding February 15, 2020 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Annual Dividend Per Share |  | CAD 1.0625 |
Percentage rate used to determine dividend rate |  | 2.63% |
Outstanding share redemption price per share |  | CAD 25 |
Series F Preferred Stock [Member] |  |  |
Class of Stock [Line Items] |  |  |
Amount per share used to determine dividend per share |  | CAD 25 |
Term of Canada government bond yield |  | 5 years |
Series F Preferred Stock [Member] | Up To And Excluding August 15, 2020 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Annual Dividend Per Share |  | CAD 0.6388 |
Percentage rate used to determine dividend rate |  | 1.84% |
Outstanding share redemption price per share |  | CAD 25 |
Series F Preferred Stock [Member] | Up To And Excluding August 15, 2018 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Annual Dividend Per Share |  | CAD 1.025 |
Percentage rate used to determine dividend rate |  | 2.65% |
Outstanding share redemption price per share |  | CAD 25 |
Series F Preferred Stock [Member] | Up To And Excluding February 15, 2020 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Annual Dividend Per Share |  | CAD 1.0625 |
Percentage rate used to determine dividend rate |  | 2.63% |
Outstanding share redemption price per share |  | CAD 25 |
Series D Preferred Stock [Member] | August 15, 2020 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25 |
Series D Preferred Stock [Member] | August 15, 2023 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25 |
Series D Preferred Stock [Member] | February 15, 2025 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25 |
Series D Preferred Stock [Member] | After August 15, 2015 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25.5 |
Series D Preferred Stock [Member] | After August 15, 2018 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25.5 |
Series D Preferred Stock [Member] | After February 15, 2020 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25.5 |
Series G Preferred Stock [Member] | August 15, 2020 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25 |
Series G Preferred Stock [Member] | August 15, 2023 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25 |
Series G Preferred Stock [Member] | February 15, 2025 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25 |
Series G Preferred Stock [Member] | After August 15, 2015 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25.5 |
Series G Preferred Stock [Member] | After August 15, 2018 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25.5 |
Series G Preferred Stock [Member] | After February 15, 2020 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25.5 |
Series E Preferred Stock [Member] |  |  |
Class of Stock [Line Items] |  |  |
Annual Dividend Per Share |  | 1.125 |
Series E Preferred Stock [Member] | If Redeemed Prior To August 15, 2019 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 26 |
Series E Preferred Stock [Member] | If Redeemed On Or After August 15, 2019, But Prior To August 15, 2020 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25.75 |
Series E Preferred Stock [Member] | If Redeemed On Or After August 15, 2020, But Prior To August 15, 2021 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25.5 |
Series E Preferred Stock [Member] | If Redeemed On Or After August 15, 2021, But Prior To August 15, 2022 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | 25.25 |
Series E Preferred Stock [Member] | If Redeemed On Or After August 15, 2022 [Member] |  |  |
Class of Stock [Line Items] |  |  |
Outstanding share redemption price per share |  | CAD 25 |

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- Definition The number of shares converted in a noncash (or part noncash) transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4313-108586 + Details
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