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Common Stock (Common Stock Rollfoward) (Details) - CAD ($) shares in Thousands, $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018
Increase (Decrease) In Common Stock Value [Roll Forward] |  |
Balance, December 31, 2018 | $ 5,816 |
Issuance of common stock |  | $ 25
Issuance of common stock | 99 | 295
Options exercised under senior management share option plan | 97 |
Balance, December 31, 2019 | $ 6,216 | $ 5,816
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |
Balance, December 31, 2018 | 234,120 | 228,770
Conversion of Convertible Debentures | 30 | 10
Issuance of common stock | 1,770 | 450
Issued under Purchase Plans at market rate | 3,990 | 4,870
Discount on shares purchased under Dividend Reinvestment Plan | 0 | 0
Options exercised under senior management share option plan | 2,570 | 20
Employee Share Purchase Plan | 0 | 0
Balance, December 31, 2019 | 242,480 | 234,120
Common Stock |  |
Increase (Decrease) In Common Stock Value [Roll Forward] |  |
Balance, December 31, 2018 | $ 5,816 | $ 5,601
Conversion of Convertible Debentures | 1 | 0
Issuance of common stock |  | 22
Issuance of common stock | 99 | 0
Issued under Purchase Plans at market rate | 202 | 200
Discount on shares purchased under Dividend Reinvestment Plan Value | 7 | 9
Options exercised under senior management share option plan | 104 | 1
Employee Share Purchase Plan | 1 | 1
Balance, December 31, 2019 | $ 6,216 | $ 5,816

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