Supplemental Information (Derivatives and Hedging) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivative assets	$ 4,332	$ 5,467
Derivative liabilities	3,717	4,883
Netting adjustment of derivative gross asset	(2,169)	(3,097)
Netting adjustment of derivative gross liability	(2,165)	(3,094)
Cash collateral assets	(934)	(672)
Net derivative assets	793	1,113
Net derivative liabilities	760	410
Cumulative gain (loss) adjustment for non performance risk	(3)	(3)
Excluded excess cash collateral received	151	6
Excluded excess cash collateral posted	317	177
Excluded excess securities collateral received	35	0
Derivatives Accounted For As Hedges
Derivatives, Fair Value [Line Items]
Derivative assets	2,926	3,508
Derivative liabilities	521	834
Derivatives Not Accounted For As Hedges
Derivatives, Fair Value [Line Items]
Derivative assets	1,406	1,958
Derivative liabilities	3,195	4,048
Interest Rate Contracts | Derivatives Accounted For As Hedges
Derivatives, Fair Value [Line Items]
Derivative assets	2,818	3,106
Derivative liabilities	161	210
Interest Rate Contracts | Derivatives Not Accounted For As Hedges
Derivatives, Fair Value [Line Items]
Derivative assets	51	62
Derivative liabilities	14	20
Currency Exchange Contracts | Derivatives Accounted For As Hedges
Derivatives, Fair Value [Line Items]
Derivative assets	108	402
Derivative liabilities	360	624
Currency Exchange Contracts | Derivatives Not Accounted For As Hedges
Derivatives, Fair Value [Line Items]
Derivative assets	1,244	1,778
Derivative liabilities	3,164	4,011
Other Contracts | Derivatives Accounted For As Hedges
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	110	119
Derivative liabilities	17	17
Gross Accrued Interest [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	330	768
Derivative liabilities	(22)	(24)
Gross Derivatives [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	4,662	6,234
Derivative liabilities	3,695	4,859
Amounts Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(3,869)	(5,121)
Derivative liabilities	(2,935)	(4,449)
Cash collateral assets	(1,700)	(2,025)
Cash collateral liabilities	(770)	(1,355)
Securities Pledged as Collateral [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(323)	(442)
Derivative liabilities	0	0
Net Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	470	671
Derivative liabilities	$ 760	$ 410