Derivative contracts (Detail) (Finance and Financial Products [Member], Not Designated as Hedging Instrument [Member], USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Derivative [Line Items]
Counterparty netting - liabilities	$ (39)		$ (43)
Liabilities	10,137		10,139
Equity Index Put Options [Member]
Derivative [Line Items]
Liabilities	8,983		8,499
Notional Value	33,463	[1]	34,014	[1]
Credit Default Contracts - High Yield Indexes [Member]
Derivative [Line Items]
Liabilities	15		198
Notional Value	3,258	[2]	4,568	[2]
Credit Default Contracts - States and Municipalities [Member]
Derivative [Line Items]
Liabilities	953		1,297
Notional Value	16,042	[2]	16,042	[2]
Credit Default Contracts - Individual Corporate [Member]
Derivative [Line Items]
Liabilities	19		32
Notional Value	3,565	[2]	3,565	[2]
Other Derivative [Member]
Derivative [Line Items]
Liabilities	206		156
Other Assets [Member]
Derivative [Line Items]
Counterparty netting - assets	(61)	[3]	(67)	[3]
Assets	219	[3]	256	[3]
Other Assets [Member] | Credit Default Contracts - Individual Corporate [Member]
Derivative [Line Items]
Assets	60	[3]	55	[3]
Other Assets [Member] | Other Derivative [Member]
Derivative [Line Items]
Assets	$ 220	[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. 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.