Supplemental Information (Derivatives and Hedging) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Derivative assets	$ 6,976	$ 7,391
Derivative liabilities	3,988	5,681
Netting adjustment of derivative gross asset	(2,367)	(4,326)
Netting adjustment of derivative gross liability	(2,358)	(4,326)
Cash collateral assets	(3,232)	(1,141)
Net derivative assets	1,219	2,282
Net derivative liabilities	723	700
Cumulative gain (loss) adjustment for non performance risk	(9)
Excluded excess cash collateral received	188	48
Excluded excess cash collateral posted	0	379
Total Fair Value of Collateral	4,895
Designated As Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	5,642	5,241
Derivative liabilities	437	1,541
Derivatives Not Accounted For As Hedges
Derivatives, Fair Value [Line Items]
Derivative assets	1,334	2,149
Derivative liabilities	3,550	4,141
Interest Rate Contracts | Designated As Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	5,411	4,132
Derivative liabilities	23	158
Interest Rate Contracts | Derivatives Not Accounted For As Hedges
Derivatives, Fair Value [Line Items]
Derivative assets	128	119
Derivative liabilities	23	44
Currency Exchange Contracts | Designated As Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	231	1,109
Derivative liabilities	414	1,383
Currency Exchange Contracts | Derivatives Not Accounted For As Hedges
Derivatives, Fair Value [Line Items]
Derivative assets	1,111	1,715
Derivative liabilities	3,506	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	96	315
Derivative liabilities	22	49
Gross Accrued Interest [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	764	1,001
Derivative liabilities	24	(13)
Gross Derivatives [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	7,740	8,392
Derivative liabilities	4,012	5,668
Amounts Offset In Statement Of Financial Position [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(6,521)	(6,110)
Derivative liabilities	(3,289)	(4,968)
Cash collateral assets	(4,154)	(1,784)
Cash collateral liabilities	(931)	(642)
Securities Pledged as Collateral [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	(741)	(1,277)
Derivative liabilities	0	0
Net Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	478	1,005
Derivative liabilities	$ 723	$ 700