Derivative contracts - gains and losses (Detail) (Finance and Financial Products [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	$ (2,104)	$ 261	$ 3,624
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	(2,104)	261	3,624
Not Designated as Hedging Instrument [Member] | Equity Index Put Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	(1,787)	172	2,713
Not Designated as Hedging Instrument [Member] | Credit Default Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	(251)	250	789
Not Designated as Hedging Instrument [Member] | Other Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains/losses	$ (66)	$ (161)	$ 122