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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	$ 427	$ (118)	$ 2,094	$ (184)
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	427	(118)	2,094	(184)
Not Designated as Hedging Instrument [Member] | Equity Index Put Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	519	(534)	2,155	(1,018)
Not Designated as Hedging Instrument [Member] | Credit Default Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	(128)	316	(43)	827
Not Designated as Hedging Instrument [Member] | Other, principally interest rate and foreign currency [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	$ 36	$ 100	$ (18)	$ 7