Financial Instruments (Fair value hedges) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Fair value hedges
Hedge amount excluded from assessment of effectiveness	insignificant amounts	insignificant amounts
Cash Flow Hedge [Member]
Fair value hedges
Hedge ineffectiveness gain (loss)	4	31
Hedge amount excluded from assessment of effectiveness	insignificant gains and losses	insignificant gains and losses
Net Investment Hedge [Member]
Fair value hedges
Hedge ineffectiveness gain (loss)	(874)	(1,345)
Free Standing Derivatives [Member]
Fair value hedges
Gain (loss) on derivatives	(608)	(667)
Fair Value Hedges [Member]
Fair value hedges
Hedge ineffectiveness gain (loss)	(303)	(459)
Interest Rate Contract [Member] | Free Standing Derivatives [Member]
Fair value hedges
Gain (loss) on derivatives	(291)	(25)
Interest Rate Contract [Member] | Fair Value Hedges [Member]
Fair value hedges
Gain (loss) on derivatives	708	5,888
Gain (loss) on hedged items	(1,041)	(6,322)
Foreign Exchange Contract [Member] | Free Standing Derivatives [Member]
Fair value hedges
Gain (loss) on derivatives	(310)	(666)
Foreign Exchange Contract [Member] | Fair Value Hedges [Member]
Fair value hedges
Gain (loss) on derivatives	(169)	119
Gain (loss) on hedged items	199	(144)
Other Contract [Member] | Free Standing Derivatives [Member]
Fair value hedges
Gain (loss) on derivatives	(7)	24