Derivative contracts (Detail) - Finance and Financial Products [Member] - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Liabilities		$ 4,646	$ 3,836
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Liabilities		4,646	3,836
Not Designated as Hedging Instrument [Member] | Equity Index Put Options [Member]
Derivative [Line Items]
Liabilities		4,348	3,552
Notional Value	[1]	28,356	27,722
Not Designated as Hedging Instrument [Member] | Credit Default [Member]
Derivative [Line Items]
Liabilities		298	284
Notional Value	[2]	$ 7,792	$ 7,792

[1] Represents the aggregate undiscounted amounts payable assuming that the value of each index is zero at each contract's expiration date. Certain of these contracts are denominated in foreign currencies. Notional amounts are based on the foreign currency exchange rates as of each balance sheet 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.