Financial Derivatives (Total Derivatives) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative, Notional Amount	$ 418,625	$ 410,803
Derivative Asset, Fair Value	2,874	4,616
Derivative Liability, Fair Value	2,856	3,839
Derivative Asset, Fair Value Offset Amount	(1,054)	(2,460)
Derivative Asset, Cash Collateral	(636)	(657)
Derivative Asset, Net Fair Value	1,184	1,499
Derivative Liability, Fair Value Offset Amount	(1,054)	(2,460)
Derivative Liability, Cash Collateral	(763)	(484)
Derivative Liability, Net Fair Value	1,039	895
Increase (Decrease) in Derivative Assets	(800)
Increase (Decrease) in Derivative Liabilities	(700)
Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Notional Amount	58,994	55,786
Derivative Asset, Fair Value	174	889
Derivative Liability, Fair Value	111	285
Designated as Hedging Instrument | Fair Value Hedging | Interest Rate Contract
Derivative [Line Items]
Derivative, Notional Amount	34,059	34,010
Derivative Asset, Fair Value	114	551
Derivative Liability, Fair Value	94	214
Designated as Hedging Instrument | Cash Flow Hedging | Interest Rate Contract
Derivative [Line Items]
Derivative, Notional Amount	23,875	20,831
Derivative Asset, Fair Value	60	313
Derivative Liability, Fair Value	6	71
Designated as Hedging Instrument | Net Investment Hedging | Foreign Exchange Contract
Derivative [Line Items]
Derivative, Notional Amount	1,060	945
Derivative Asset, Fair Value		25
Derivative Liability, Fair Value	11
Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Notional Amount	359,631	355,017
Derivative Asset, Fair Value	2,700	3,727
Derivative Liability, Fair Value	2,745	3,554
Not Designated as Hedging Instrument | Mortgage Banking | Interest Rate Contract
Derivative [Line Items]
Derivative, Notional Amount	107,358	130,559
Derivative Asset, Fair Value	192	907
Derivative Liability, Fair Value	53	565
Not Designated as Hedging Instrument | Mortgage Banking | Swap | Interest Rate Contract
Derivative [Line Items]
Derivative, Notional Amount	48,335	49,071
Derivative Asset, Fair Value	162	783
Derivative Liability, Fair Value	42	505
Not Designated as Hedging Instrument | Mortgage Banking | Future | Interest Rate Contract
Derivative [Line Items]
Derivative, Notional Amount	47,494	36,264
Not Designated as Hedging Instrument | Mortgage Banking | Mortgage Commitment | Interest Rate Contract
Derivative [Line Items]
Derivative, Notional Amount	8,999	13,317
Derivative Asset, Fair Value	19	96
Derivative Liability, Fair Value	9	56
Not Designated as Hedging Instrument | Mortgage Banking | Other Contract | Interest Rate Contract
Derivative [Line Items]
Derivative, Notional Amount	2,530	31,907
Derivative Asset, Fair Value	11	28
Derivative Liability, Fair Value	2	4
Not Designated as Hedging Instrument | Customer Contracts
Derivative [Line Items]
Derivative, Notional Amount	244,828	218,877
Derivative Asset, Fair Value	2,505	2,780
Derivative Liability, Fair Value	2,142	2,584
Not Designated as Hedging Instrument | Customer Contracts | Interest Rate Contract
Derivative [Line Items]
Derivative, Notional Amount	217,498	196,988
Derivative Asset, Fair Value	2,156	2,438
Derivative Liability, Fair Value	1,810	2,275
Not Designated as Hedging Instrument | Customer Contracts | Foreign Exchange And Other Contract
Derivative [Line Items]
Derivative, Notional Amount	27,330	21,889
Derivative Asset, Fair Value	349	342
Derivative Liability, Fair Value	332	309
Not Designated as Hedging Instrument | Customer Contracts | Swap | Interest Rate Contract
Derivative [Line Items]
Derivative, Notional Amount	194,042	173,777
Derivative Asset, Fair Value	2,079	2,373
Derivative Liability, Fair Value	1,772	2,214
Not Designated as Hedging Instrument | Customer Contracts | Future | Interest Rate Contract
Derivative [Line Items]
Derivative, Notional Amount	3,453	4,053
Not Designated as Hedging Instrument | Customer Contracts | Mortgage Commitment | Interest Rate Contract
Derivative [Line Items]
Derivative, Notional Amount	2,228	2,955
Derivative Asset, Fair Value	2	10
Derivative Liability, Fair Value	2	8
Not Designated as Hedging Instrument | Customer Contracts | Other Contract | Interest Rate Contract
Derivative [Line Items]
Derivative, Notional Amount	17,775	16,203
Derivative Asset, Fair Value	75	55
Derivative Liability, Fair Value	36	53
Not Designated as Hedging Instrument | Other Risk Management Activity | Foreign Exchange And Other Contract
Derivative [Line Items]
Derivative, Notional Amount	7,445	5,581
Derivative Asset, Fair Value	3	40
Derivative Liability, Fair Value	$ 550	$ 405