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Non-controlling Interest In Subsidiaries (Preferred shares of GBPC) (Details) - CAD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Noncontrolling Interest [Line Items] |  |
Number of shares issued and outstanding | 41,000,000 | 41,000,000
Non-voting Cumulative Redeemable Variable Perpetual Preferred Shares | GBPC |  |
Noncontrolling Interest [Line Items] |  |
Preferred Stock, Shares Authorized | 10,000 |
Number of shares issued and outstanding | 10,000 | 10,000
Outstanding as at December 31 | $ 14 | $ 14

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