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Common Stock (Common Stock Rollfoward) (Details) - CAD ($) shares in Thousands, $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Increase (Decrease) In Common Stock Value [Roll Forward] |  |
Beginning Balance | $ 6,216 |
Issuance of common stock | 251 | $ 99
Options exercised under senior management share option plan | 19 | 97
Ending Balance | $ 6,705 | $ 6,216
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |
Beginning Balance | 242,480 | 234,120
Conversion of Convertible Debentures | 0 | 30
Issuance of common stock | 4,540 | 1,770
Issued under Purchase Plans at market rate | 3,990 | 3,990
Discount on shares purchased under Dividend Reinvestment Plan | 0 | 0
Options exercised under senior management share option plan | 420 | 2,570
Employee Share Purchase Plan | 0 | 0
Ending Balance | 251,430 | 242,480
Common Stock |  |
Increase (Decrease) In Common Stock Value [Roll Forward] |  |
Beginning Balance | $ 6,216 | $ 5,816
Conversion of Convertible Debentures | 0 | 1
Issuance of common stock | 251 | 99
Issued under Purchase Plans at market rate | 219 | 202
Discount on shares purchased under Dividend Reinvestment Plan Value | (4) | (7)
Options exercised under senior management share option plan | 20 | 104
Employee Share Purchase Plan | 3 | 1
Ending Balance | $ 6,705 | $ 6,216

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