Derivative contracts (Detail) (Finance and Financial Products [Member], Not Designated as Hedging Instrument [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Derivative [Line Items]
Liabilities	$ 7,933		$ 10,139
Counterparty netting - liabilities			(43)
Equity Index Put Options [Member]
Derivative [Line Items]
Liabilities	7,502		8,499
Notional Value	33,357	[1]	34,014	[1]
Credit Default Contracts [Member]
Derivative [Line Items]
Liabilities	429		1,527
Notional Value	11,691	[2]	24,194	[2]
Other, principally interest rate and foreign currency [Member]
Derivative [Line Items]
Liabilities	2		156
Other Assets [Member]
Derivative [Line Items]
Assets	171	[3]	256	[3]
Counterparty netting - assets			(67)	[3]
Other Assets [Member] | Credit Default Contracts [Member]
Derivative [Line Items]
Assets	41	[3]	55	[3]
Other Assets [Member] | Other, principally interest rate and foreign currency [Member]
Derivative [Line Items]
Assets	$ 130	[3]	$ 268	[3]

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

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