Derivative contracts - gains and losses (Detail) - Finance and Financial Products [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	$ (764)	$ 258	$ 380	$ 649
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	(764)	258	380	649
Not Designated as Hedging Instrument [Member] | Equity Index Put Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	(802)	223	371	156
Not Designated as Hedging Instrument [Member] | Credit Default [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	$ 38	$ 35	$ 9	492
Not Designated as Hedging Instrument [Member] | Other, Principally Interest Rate and Foreign Currency [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses				$ 1