Derivative contracts (Detail) - Finance and Financial Products [Member] - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Liabilities		$ 4,430	$ 4,810
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Liabilities		4,430	4,810
Not Designated as Hedging Instrument [Member] | Equity Index Put Options [Member]
Derivative [Line Items]
Liabilities		4,188	4,560
Notional Value	[1]	28,239	29,469
Not Designated as Hedging Instrument [Member] | Credit Default [Member]
Derivative [Line Items]
Liabilities		242	250
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 aggregate undiscounted amounts payable under the contracts assuming all underlying issuers default and the residual value of the specified obligations is zero.