Financial Instruments (Derivatives and hedging) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	$ 294,000
Derivative asset, fair value	873	180
Derivative liability, fair value	283	166
Cumulative gain (loss) adjustment for non performance risk	18	15
Excess Collateralization	78	42
Excess Collateral Posted	13	10
Excess Securities Collateral Held	97	359
Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	11,598	12,897
Derivative liabilities	3,103	3,074
Amounts Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(6,354)	(7,657)
Derivative liabilities	(2,820)	(2,908)
Netting Adjustment [Member] | Amounts Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Netting adjustment of derivative gross asset	(2,626)	(2,532)
Netting adjustment of derivative gross liability	(2,608)	(2,517)
Cash Collateral [Member] | Amounts Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Cash collateral assets	(3,728)	(5,125)
Cash collateral liabilities	(212)	(391)
Securities Pledged as Collateral [Member] | Not Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(4,371)	(5,060)
Derivative liabilities	0	0
Derivatives Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	8,874	9,270
Derivative liabilities	1,576	2,481
Derivatives Not Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	1,466	1,944
Derivative liabilities	1,511	579
Derivatives Associated With Interest Rate, Currency Or Market Risk Reduction Or Elimination [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	286,000
Percentage Of Notional Amount That Is Associated With Reducing Or Eliminating Interest Rate, Currency, Or Market Risk	97.00%
Gross Derivatives [Member] | Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	10,340	11,214
Derivative liabilities	3,087	3,060
Gross Accrued Interest [Member] | Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	1,258	1,683
Derivative liabilities	16	14
Net Derivative [Member] | Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	5,244	5,240
Derivative liabilities	283	166
Interest Rate Contract [Member] | Derivatives Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	7,055	8,443
Derivative liabilities	691	719
Interest Rate Contract [Member] | Derivatives Not Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	386	452
Derivative liabilities	180	195
Foreign Exchange Contract [Member] | Derivatives Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	1,819	827
Derivative liabilities	885	1,762
Foreign Exchange Contract [Member] | Derivatives Not Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	1,037	1,457
Derivative liabilities	1,306	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	43	35
Derivative liabilities	$ 25	$ 26