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Income Taxes - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Income Tax Disclosure [Abstract]        
Effective tax rate 27.40% 13.30% 24.50% 13.10%
IRS        
Income Tax Examination [Line Items]        
Possible increase in U.S. taxable income     $ 696  
Possible additional federal tax expense     $ 244