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 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in Income $ (69) $ (6) $ (47) $ 24
Interest rate contracts | Interest Expense        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in Income (2) (2) (4) (4)
Foreign exchange contracts | Investment income and other        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in Income (67) 14 (59) 20
Investment market price contracts | Investment income and other        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in Income $ 0 $ (18) $ 16 $ 8