Derivative contracts (Detail) (Finance and Financial Products [Member], Not Designated as Hedging Instrument [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Derivative [Line Items]
Liabilities	$ 5,847		$ 7,933
Equity Index Put Options [Member]
Derivative [Line Items]
Liabilities	5,355		7,502
Notional Value	31,925	[1]	33,357	[1]
Credit Default Contracts [Member]
Derivative [Line Items]
Liabilities	478		429
Notional Value	8,510	[2]	11,691	[2]
Other, principally interest rate and foreign currency [Member]
Derivative [Line Items]
Liabilities	14		2
Other Assets [Member]
Derivative [Line Items]
Assets	12	[3]	171	[3]
Other Assets [Member] | Credit Default Contracts [Member]
Derivative [Line Items]
Assets	4	[3]	41	[3]
Other Assets [Member] | Other, principally interest rate and foreign currency [Member]
Derivative [Line Items]
Assets	$ 8	[3]	$ 130	[3]

[1] Represents the aggregate undiscounted amount payable at the contract expiration dates assuming that the value of each 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.

[3] Included in other assets of finance and financial products businesses.