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Legal Settlements and Loss Contingencies - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Dec. 31, 2018
Loss Contingencies [Line Items]          
Legal settlements and loss contingencies, expenses $ 468 $ 19 $ 1,171 $ 1,239  
Accrued amount for legal settlements and loss contingencies $ 1,601   $ 1,601   $ 562