Quarterly report pursuant to Section 13 or 15(d)

Amount Recorded in Income Statements for Foreign Currency Forward Contracts Not Designated as Hedges (Detail)

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Amount Recorded in Income Statements for Foreign Currency Forward Contracts Not Designated as Hedges (Detail) - Not Designated as Hedging Instrument - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in Income $ (17) $ (33) $ (64) $ (9)
Interest rate contracts | Interest Expense        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in Income (3) (2) (7) (6)
Foreign exchange contracts | Investment income and other        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in Income (14) 14 (73) 34
Investment market price contracts | Investment income and other        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in Income $ 0 $ (45) $ 16 $ (37)