Derivative contracts - gains and losses (Detail) (Finance and Financial Products [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	$ 236	$ 1,206
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	236	1,206
Not Designated as Hedging Instrument [Member] | Equity Index Put Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	(132)	1,246
Not Designated as Hedging Instrument [Member] | Credit Default Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	373	(14)
Not Designated as Hedging Instrument [Member] | Other, principally interest rate and foreign currency [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	$ (5)	$ (26)