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Common Shares - Additional Information (Detail) - shares
Jun. 29, 2020
Jun. 15, 2020
Jun. 28, 2021
Class of Stock [Line Items]      
Normal course issuer bid share repurchase shares authorized 50,000    
Exxon Mobil Corporation's ownership interest in Imperial 69.60%    
Normal course issuer bid share repurchase term, months 12 months    
Percentage of total number of common shares   4.00%  
Subsequent Event [Member] | Maximum [Member]      
Class of Stock [Line Items]      
Normal course issuer bid share repurchase shares authorized     29,363,070