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Non-controlling Interest In Subsidiaries (Preferred shares of GBPC) (Details) - CAD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
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 20,000
Outstanding as at December 31 $ 14 $ 19