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Leases - Additional Information (Detail) - CAD ($)
$ in Millions
 12 Months Ended
Jan. 01, 2019
Dec. 31, 2020
Dec. 31, 2019
Leases Disclosure [Line Items]      
Cash outflow in relation to lease obligation   $ 9 $ 10
Deferred base rent balance $ 3    
Real Estate [member] | Bottom Of Range [Member]      
Leases Disclosure [Line Items]      
Terms of operating lease commitments   1 year  
Real Estate [member] | Top of Range [Member]      
Leases Disclosure [Line Items]      
Terms of operating lease commitments   10 years  
Vehicles [member] | Bottom Of Range [Member]      
Leases Disclosure [Line Items]      
Terms of operating lease commitments   3 years  
Vehicles [member] | Top of Range [Member]      
Leases Disclosure [Line Items]      
Terms of operating lease commitments   4 years  
Rig Equipment [Member]      
Leases Disclosure [Line Items]      
Long-term drilling contracts   $ 477 $ 1,000
Rig Equipment [Member] | Bottom Of Range [Member]      
Leases Disclosure [Line Items]      
Term of operating leases under long term drilling contracts   1 year  
Rig Equipment [Member] | Top of Range [Member]      
Leases Disclosure [Line Items]      
Term of operating leases under long term drilling contracts   5 years