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Pension Plans and Other Postretirement Benefits - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Compensation And Retirement Disclosure [Abstract]        
Defined contribution pension and retirement savings plans total expense $ 23 $ 23 $ 81 $ 73