Derivative contracts (Detail) (Finance and Financial Products [Member], Not Designated as Hedging Instrument [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Derivative [Line Items]
Liabilities	$ 5,095		$ 5,331
Equity Index Put Options [Member]
Derivative [Line Items]
Liabilities	4,800		4,667
Notional Value	32,225	[1]	32,095	[1]
Credit Default Contracts [Member]
Derivative [Line Items]
Liabilities	275		648
Notional Value	7,792	[2]	7,792	[2]
Other, principally interest rate and foreign currency [Member]
Derivative [Line Items]
Liabilities	$ 20		$ 16

[1] Represents the aggregate undiscounted amount payable at the contract expiration dates assuming that the value of the related index is zero at each contract's expiration date.

[2] Represents the maximum undiscounted future value of losses payable under the contracts, if all underlying issuers default and the residual value of the specified obligations is zero.