Derivative contracts - gains and losses (Detail) (Finance and Financial Products [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	$ 258	$ 427	$ 649	$ 2,094
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	258	427	649	2,094
Not Designated as Hedging Instrument [Member] | Equity Index Put Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	223	519	156	2,155
Not Designated as Hedging Instrument [Member] | Credit Default Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	35	(128)	492	(43)
Not Designated as Hedging Instrument [Member] | Other, principally interest rate and foreign currency [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses		$ 36	$ 1	$ (18)