Derivative contracts (Detail) (Finance and Financial Products [Member], USD $) In Millions, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Derivative [Line Items]
Liabilities	$ 4,925		$ 5,331
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Liabilities	4,925		5,331
Not Designated as Hedging Instrument [Member] | Equity Index Put Options [Member]
Derivative [Line Items]
Liabilities	4,734		4,667
Notional value	32,362	[1]	32,095	[1]
Not Designated as Hedging Instrument [Member] | Credit Default Contracts [Member]
Derivative [Line Items]
Liabilities	191		648
Notional value	7,792	[2]	7,792	[2]
Not Designated as Hedging Instrument [Member] | Other, principally interest rate and foreign currency [Member]
Derivative [Line Items]
Liabilities			$ 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.