Derivative contracts (Detail) (Finance and Financial Products [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Derivative [Line Items]
Liabilities	$ 3,503		$ 4,810
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Liabilities	3,503		4,810
Not Designated as Hedging Instrument [Member] | Equity Index Put Options [Member]
Derivative [Line Items]
Liabilities	3,249		4,560
Notional Value	27,604	[1]	29,469	[1]
Not Designated as Hedging Instrument [Member] | Credit Default Contracts [Member]
Derivative [Line Items]
Liabilities	243		250
Notional Value	7,792	[2]	7,792	[2]
Not Designated as Hedging Instrument [Member] | Other [Member]
Derivative [Line Items]
Liabilities	$ 11

[1] Represents the aggregate undiscounted amounts payable assuming that the value of each index is zero at each contract's expiration date. Notional amounts are based on the foreign currency exchange rates as of each balance sheet date. In the first quarter of 2015, the aggregate notional value declined as a result of foreign currency exchange rate changes applicable to certain of the contracts.

[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.