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Financing and Additional Notes and Loans Payable Information - Additional Information (Detail) - CAD ($)
1 Months Ended
Dec. 31, 2019
Nov. 30, 2019
Nov. 29, 2019
Long Term Line Of Credit      
Financing Activities [Line Items]      
Non-interest bearing, revolving demand loan, outstanding amount   $ 0  
Debt instrument, maturity date   Nov. 30, 2021  
Non-interest bearing, revolving demand loan, remaining borrowing capacity   $ 250,000,000  
Short Term Line of Credit      
Financing Activities [Line Items]      
Non-interest bearing, revolving demand loan, outstanding amount $ 0    
Debt instrument, maturity date Dec. 31, 2020    
Non-interest bearing, revolving demand loan, remaining borrowing capacity $ 250,000,000    
Exxon Mobil | Revolving demand loan      
Financing Activities [Line Items]      
Non-interest bearing, revolving demand loan, maximum borrowing capacity   $ 150,000,000 $ 75,000,000
Non-interest bearing, revolving demand loan, outstanding amount $ 111,000,000