Financial Instruments (Derivatives and hedging) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	$ 287,000
Derivative asset, fair value	174	180
Derivative liability, fair value	619	166
Cumulative gain (loss) adjustment for non performance risk	(14)	(15)
Excess Collateralization	47	42
Excess Collateral Posted	28	10
Excess Securities Collateral Held	22	359
Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	9,026	12,897
Derivative liabilities	4,553	3,074
Amounts Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(6,806)	(7,657)
Derivative liabilities	(3,934)	(2,908)
Netting Adjustment [Member] | Amounts Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Netting adjustment of derivative gross asset	(3,642)	(2,532)
Netting adjustment of derivative gross liability	(3,628)	(2,517)
Cash Collateral [Member] | Amounts Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Cash collateral assets	(3,164)	(5,125)
Cash collateral liabilities	(306)	(391)
Securities Pledged as Collateral [Member] | Not Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(2,046)	(5,060)
Derivative liabilities	0	0
Derivatives Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	6,313	9,270
Derivative liabilities	3,087	2,481
Derivatives Not Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	1,527	1,944
Derivative liabilities	1,679	579
Derivatives Associated With Interest Rate, Currency Or Market Risk Reduction Or Elimination [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	277,000
Percentage Of Notional Amount That Is Associated With Reducing Or Eliminating Interest Rate, Currency, Or Market Risk	96.00%
Gross Derivatives [Member] | Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	7,840	11,214
Derivative liabilities	4,766	3,060
Gross Accrued Interest [Member] | Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	1,186	1,683
Derivative liabilities	(213)	14
Net Derivative [Member] | Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	2,220	5,240
Derivative liabilities	619	166
Interest Rate Contract [Member] | Derivatives Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	4,875	8,443
Derivative liabilities	1,621	719
Interest Rate Contract [Member] | Derivatives Not Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	348	452
Derivative liabilities	172	195
Foreign Exchange Contract [Member] | Derivatives Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	1,438	827
Derivative liabilities	1,466	1,762
Foreign Exchange Contract [Member] | Derivatives Not Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	1,133	1,457
Derivative liabilities	1,489	358
Other Contract [Member] | Derivatives Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Other Contract [Member] | Derivatives Not Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	46	35
Derivative liabilities	$ 18	$ 26