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Financial Instruments - Summary of Consolidated Financial Ratios (Detail)
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of detailed information about financial instruments [line items]      
Leverage Ratio 384.00% 385.00% 422.00%
Coverage Ratio 441.00% 346.00% 318.00%
Less than or Equal to 6.00 Ratio [member]      
Disclosure of detailed information about financial instruments [line items]      
Leverage Ratio     600.00%
Greater than or Equal to 1.85 Ratio [member]      
Disclosure of detailed information about financial instruments [line items]      
Coverage Ratio     185.00%
Less than or Equal to 5.25 Ratio [Member]      
Disclosure of detailed information about financial instruments [line items]      
Leverage Ratio   525.00%  
Greater than or Equal to 2.50 [member]      
Disclosure of detailed information about financial instruments [line items]      
Coverage Ratio 250.00% 250.00%  
Less than or Equal to 4.75 Ratio [member]      
Disclosure of detailed information about financial instruments [line items]      
Leverage Ratio 475.00%