Supplemental Information (Derivatives and Hedging) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Derivative assets	$ 7,709	$ 7,391
Derivative liabilities	4,477	5,681
Netting adjustment of derivative gross asset	(2,978)	(4,326)
Netting adjustment of derivative gross liability	(2,969)	(4,326)
Cash collateral assets	(2,991)	(1,141)
Net derivative assets	1,648	2,282
Net derivative liabilities	678	700
Cumulative gain (loss) adjustment for non performance risk	(9)
Excluded excess cash collateral received	61	48
Excluded excess cash collateral posted	79	379
Designated As Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	6,108	5,241
Derivative liabilities	653	1,541
Derivatives Not Accounted For As Hedges
Derivatives, Fair Value [Line Items]
Derivative assets	1,601	2,149
Derivative liabilities	3,823	4,141
Interest Rate Contracts | Designated As Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	5,773	4,132
Derivative liabilities	24	158
Interest Rate Contracts | Derivatives Not Accounted For As Hedges
Derivatives, Fair Value [Line Items]
Derivative assets	119	119
Derivative liabilities	101	44
Currency Exchange Contracts | Designated As Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	335	1,109
Derivative liabilities	630	1,383
Currency Exchange Contracts | Derivatives Not Accounted For As Hedges
Derivatives, Fair Value [Line Items]
Derivative assets	1,196	1,715
Derivative liabilities	3,700	4,048
Other Contracts | Designated As Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Other Contracts | Derivatives Not Accounted For As Hedges
Derivatives, Fair Value [Line Items]
Derivative assets	286	315
Derivative liabilities	23	49
Gross Accrued Interest [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	760	1,001
Derivative liabilities	32	(13)
Gross Derivatives [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	8,469	8,392
Derivative liabilities	4,509	5,668
Amounts Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(6,821)	(6,110)
Derivative liabilities	(3,830)	(4,968)
Cash collateral assets	(3,843)	(1,784)
Cash collateral liabilities	(861)	(642)
Securities Pledged as Collateral [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(1,038)	(1,277)
Derivative liabilities	0	0
Net Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	610	1,005
Derivative liabilities	$ 678	$ 700