Derivative contracts - gains and losses (Detail) - Finance and Financial Products [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	$ 458	$ (764)	$ (332)	$ 380
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	458	(764)	(332)	380
Not Designated as Hedging Instrument [Member] | Equity Index Put Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	$ 458	(802)	(421)	371
Not Designated as Hedging Instrument [Member] | Credit Default [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses		$ 38	$ 89	$ 9