Derivative Financial Instruments (Details 8) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Notional values of derivative contracts
Notional value of derivative contracts, Total	$ 30,939	$ 40,854
Debt option [Member]
Notional values of derivative contracts
Notional amount of derivatives associated with debt carried at fair value	10,435	13,076
Interest rate swaps [Member] | Debt option [Member]
Notional values of derivative contracts
Notional amount of derivatives associated with debt carried at fair value	7,059	9,700
Currency Swap [Member] | Debt option [Member]
Notional values of derivative contracts
Notional amount of derivatives associated with debt carried at fair value	3,376	3,376
Derivatives designated as hedging instruments [Member]
Notional values of derivative contracts
Total, notional amount of derivative designated as hedge instrument	13,175	16,335
Derivatives designated as hedging instruments [Member] | Interest rate swaps [Member]
Notional values of derivative contracts
Interest rate derivatives designated as hedging instruments	6,949	8,140
Derivatives designated as hedging instruments [Member] | Currency Swap [Member]
Notional values of derivative contracts
Currency derivatives designated as hedging instruments	6,226	8,195
Derivatives not designated as hedging instruments [Member]
Notional values of derivative contracts
Notional Amount of Derivative Not Designated as Hedge Instrument	7,329	11,443
Derivatives not designated as hedging instruments [Member] | Interest rate swaps [Member]
Notional values of derivative contracts
Notional amount of interest rate derivatives not designated as hedging instruments for non-qualifying hedges	6,612	10,523
Derivatives not designated as hedging instruments [Member] | Currency Swap [Member]
Notional values of derivative contracts
Notional amount of foreign currency derivatives not designated as hedging instruments for non-qualifying economic hedges	715	715
Derivatives not designated as hedging instruments [Member] | Foreign exchange forward [Member]
Notional values of derivative contracts
Notional amount of foreign currency derivatives not designated as hedging instruments for non-qualifying economic hedges	$ 2	$ 205