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Financial Instruments - Summary of Consolidated Financial Ratios (Detail)
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of detailed information about financial instruments [line items]      
Leverage Ratio 4.07% 4.17% 3.84%
Coverage Ratio 3.82% 3.86% 4.41%
Less than or Equal to 6.25 Ratio [member]      
Disclosure of detailed information about financial instruments [line items]      
Leverage Ratio 6.25%    
Greater than or Equal to 1.75 Ratio [member]      
Disclosure of detailed information about financial instruments [line items]      
Coverage Ratio 1.75%    
Less than or Equal to 5.25 Ratio [Member]      
Disclosure of detailed information about financial instruments [line items]      
Leverage Ratio   5.25%  
Greater than or Equal to 2.50 [member]      
Disclosure of detailed information about financial instruments [line items]      
Coverage Ratio   2.50% 2.50%
Less than or Equal to 4.75 Ratio [member]      
Disclosure of detailed information about financial instruments [line items]      
Leverage Ratio 4.75%   4.75%