Financial Instruments (Derivatives and hedging) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	$ 250,000
Excess Collateralization	53	$ 58
Excess Collateral Posted	66	211
Excess Securities Collateral Held	34	385
Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	8,510	10,400
Derivative liabilities	4,398	4,203
Amounts Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(6,325)	(7,378)
Derivative liabilities	(4,378)	(4,171)
Netting Adjustment [Member] | Amounts Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(3,481)	(3,695)
Derivative liabilities	(3,483)	(3,710)
Cash Collateral [Member] | Amounts Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(2,844)	(3,683)
Derivative liabilities	(895)	(461)
Securities Pledged as Collateral [Member] | Not Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(1,510)	(3,003)
Derivative liabilities	0	0
Derivatives Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	6,961	8,294
Derivative liabilities	1,287	1,240
Derivatives Not Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	571	714
Derivative liabilities	3,102	2,987
Derivatives Associated With Interest Rate, Currency Or Market Risk Reduction Or Elimination [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	$ 247,000
Percentage Of Notional Amount That Is Associated With Reducing Or Eliminating Interest Rate, Currency, Or Market Risk	9900.00%
Gross Derivatives [Member] | Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	$ 7,532	9,008
Derivative liabilities	4,389	4,227
Gross Accrued Interest [Member] | Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	978	1,392
Derivative liabilities	9	(24)
Net Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	675	19
Derivative liabilities	20	32
Net Derivative [Member] | Recognized In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	2,185	3,022
Derivative liabilities	20	32
Interest Rate Contract | Derivatives Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	5,579	5,859
Derivative liabilities	53	461
Interest Rate Contract | Derivatives Not Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	144	111
Derivative liabilities	61	68
Foreign Exchange Contract | Derivatives Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	1,382	2,435
Derivative liabilities	1,234	779
Foreign Exchange Contract | Derivatives Not Accounted For As Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	383	595
Derivative liabilities	3,033	2,910
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	44	8
Derivative liabilities	$ 8	$ 9