Derivative contracts (Detail) (Finance and Financial Products [Member], Not Designated as Hedging Instrument [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Derivative [Line Items]
Liabilities	$ 10,139		$ 8,371
Counterparty netting - liabilities	(43)		(39)
Equity Index Put Options [Member]
Derivative [Line Items]
Liabilities	8,499		6,712
Notional Value	34,014	[1]	33,891	[1]
Credit Default Contracts - High Yield Indexes [Member]
Derivative [Line Items]
Liabilities	198		159
Notional Value	4,489	[2]	4,893	[2]
Credit Default Contracts - States and Municipalities [Member]
Derivative [Line Items]
Liabilities	1,297		1,164
Notional Value	16,042	[2]	16,042	[2]
Credit Default Contracts - Individual Corporate [Member]
Derivative [Line Items]
Liabilities	32
Notional Value	3,565	[2]	3,565	[2]
Other Derivative [Member]
Derivative [Line Items]
Liabilities	156		375
Other Assets [Member]
Derivative [Line Items]
Assets	256	[3]	343	[3]
Counterparty netting - assets	(67)	[3]	(82)	[3]
Other Assets [Member] | Credit Default Contracts - Individual Corporate [Member]
Derivative [Line Items]
Assets	55	[3]	84	[3]
Other Assets [Member] | Other Derivative [Member]
Derivative [Line Items]
Assets	$ 268	[3]	$ 341	[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. The number of losses required to exhaust contract limits under substantially all of the contracts is dependent on the loss recovery rate related to the specific obligor at the time of a default.

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