Financial Instruments (Derivatives and hedging) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	$ 336,000
Derivative asset, fair value	1,074	1,005
Derivative liability, fair value	853	1,315
Cumulative gain (loss) adjustment for non performance risk	30	(7)
Excess Collateralization	177	160
Excess Collateral Posted	56	37
Excess Securities Collateral Held	75	363
Netting Adjustment Including Collateral [Member] | Derivatives [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(6,300)	(6,739)
Derivative liabilities	(3,895)	(4,355)
Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	9,029	9,706
Derivative liabilities	4,748	5,670
Netting Adjustment [Member] | Amounts Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(3,556)	(4,120)
Derivative liabilities	(3,586)	(4,113)
Cash Collateral [Member] | Amounts Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(2,744)	(2,619)
Derivative liabilities	(309)	(242)
Securities Pledged as Collateral [Member] | Not Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(1,655)	(1,962)
Derivative liabilities	0	0
Derivatives Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	5,518	5,668
Derivative liabilities	2,535	2,973
Derivatives Not Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	2,328	2,811
Derivative liabilities	2,172	2,456
Derivatives Associated With Interest Rate, Currency Or Market Risk Reduction Or Elimination [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	293,000
Percentage Of Notional Amount That Is Associated With Reducing Or Eliminating Interest Rate, Currency, Or Market Risk	87.00%
Gross Derivatives [Member] | Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	7,846	8,479
Derivative liabilities	4,707	5,429
Gross Accrued Interest [Member] | Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	1,183	1,227
Derivative liabilities	41	241
Net Derivative [Member] | Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	2,729	2,967
Derivative liabilities	853	1,315
Interest Rate Contract [Member] | Derivatives Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	4,187	3,837
Derivative liabilities	1,350	1,989
Interest Rate Contract [Member] | Derivatives Not Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	289	270
Derivative liabilities	145	169
Foreign Exchange Contract [Member] | Derivatives Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	1,330	1,830
Derivative liabilities	1,183	984
Foreign Exchange Contract [Member] | Derivatives Not Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	1,814	2,257
Derivative liabilities	1,979	2,245
Other Contract [Member] | Derivatives Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	1	1
Derivative liabilities	2	0
Other Contract [Member] | Derivatives Not Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	225	284
Derivative liabilities	$ 48	$ 42