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Debt - 5.000% Senior Unsecured Notes Due 2027 - Additional Information (Detail) - 5.000% Senior Unsecured Notes Due 2027 [Member] - USD ($)
12 Months Ended
Sep. 07, 2017
Dec. 31, 2020
Dec. 31, 2019
Debt Instrument [Line Items]      
Senior unsecured notes face amount $ 1,400,000,000    
Senior unsecured notes, payable term   Interest on the notes is payable on April 15 and October 15 of each year.  
Senior unsecured notes, interest rate 5.00% 5.00% 5.00%
Debt instrument maturity date Oct. 15, 2027