Derivative contracts - gains and losses (Detail) (Finance and Financial Products [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	$ 1,002	$ 271
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	1,002	271
Not Designated as Hedging Instrument [Member] | Equity Index Put Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	689	223
Not Designated as Hedging Instrument [Member] | Credit Default Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	340	70
Not Designated as Hedging Instrument [Member] | Other Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	$ (27)	$ (22)