Derivative Financial Instruments - Classifications and Hedging Relationships (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	$ 321,793	$ 315,873
Derivative Asset, Fair Value, Gross	7,223	4,260
Derivative Liability, Fair Value, Gross	(3,574)	(3,336)
Derivative Asset [Abstract]
Amounts subject to master netting arrangements	(1,819)	(1,708)
Cash collateral (received) posted for amounts subject to master netting arrangements	(1,190)	(499)
Net Amount Presented in the Consolidated Balance Sheets	4,214	2,053
Derivative Liability [Abstract]
Amounts subject to master netting arrangements	1,819	1,708
Cash collateral (received) posted for amounts subject to master netting arrangements	1,307	1,262
Net amount	(448)	(366)
Fair value hedges | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	27,151	27,152
Derivative Asset, Fair Value, Gross	607	113
Derivative Liability, Fair Value, Gross	(5)	(27)
Fair value hedges | Interest rate contracts | Swap | Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	23,701	23,701
Derivative Asset, Fair Value, Gross	607	113
Derivative Liability, Fair Value, Gross	0	(25)
Fair value hedges | Interest rate contracts | Swap | Commercial Loan [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	43	44
Derivative Asset, Fair Value, Gross	0	0
Derivative Liability, Fair Value, Gross	0	0
Fair value hedges | Interest rate contracts | Options | Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	3,407	3,407
Derivative Asset, Fair Value, Gross	0	0
Derivative Liability, Fair Value, Gross	(5)	(2)
Not designated as hedges
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	294,642	288,721
Derivative Asset, Fair Value, Gross	6,616	4,147
Derivative Liability, Fair Value, Gross	(3,569)	(3,309)
Not designated as hedges | Client-related and other risk management
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	248,893	244,317
Derivative Asset, Fair Value, Gross	6,379	4,077
Derivative Liability, Fair Value, Gross	(3,483)	(3,282)
Not designated as hedges | Client-related and other risk management | Interest rate contracts | Swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	150,930	144,473
Derivative Asset, Fair Value, Gross	4,179	1,817
Derivative Liability, Fair Value, Gross	(1,002)	(673)
Not designated as hedges | Client-related and other risk management | Interest rate contracts | Options
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	25,159	25,938
Derivative Asset, Fair Value, Gross	68	28
Derivative Liability, Fair Value, Gross	(22)	(19)
Not designated as hedges | Client-related and other risk management | Interest rate contracts | Forward commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	3,952	7,907
Derivative Asset, Fair Value, Gross	13	6
Derivative Liability, Fair Value, Gross	(12)	(7)
Not designated as hedges | Client-related and other risk management | Interest rate contracts | Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	2,782	1,807
Derivative Asset, Fair Value, Gross	0	0
Derivative Liability, Fair Value, Gross	0	0
Not designated as hedges | Client-related and other risk management | Equity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	40,737	38,426
Derivative Asset, Fair Value, Gross	1,669	1,988
Derivative Liability, Fair Value, Gross	(2,048)	(2,307)
Not designated as hedges | Client-related and other risk management | Credit Contract | Loans and leases
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	744	894
Derivative Asset, Fair Value, Gross	0	0
Derivative Liability, Fair Value, Gross	(7)	(34)
Not designated as hedges | Client-related and other risk management | Credit Contract | Risk participation agreements
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	7,978	6,696
Derivative Asset, Fair Value, Gross	0	0
Derivative Liability, Fair Value, Gross	(11)	(2)
Not designated as hedges | Client-related and other risk management | Credit Contract | Total Return Swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	1,543	2,531
Derivative Asset, Fair Value, Gross	95	27
Derivative Liability, Fair Value, Gross	(17)	(11)
Not designated as hedges | Client-related and other risk management | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	12,247	12,986
Derivative Asset, Fair Value, Gross	149	144
Derivative Liability, Fair Value, Gross	(162)	(164)
Not designated as hedges | Client-related and other risk management | Commodity Contract
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	2,821	2,659
Derivative Asset, Fair Value, Gross	206	67
Derivative Liability, Fair Value, Gross	(202)	(65)
Not designated as hedges | Mortgage banking | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	23,826	17,562
Derivative Asset, Fair Value, Gross	218	46
Derivative Liability, Fair Value, Gross	(86)	(20)
Not designated as hedges | Mortgage banking | Interest rate contracts | Swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	422	535
Derivative Asset, Fair Value, Gross	0	0
Derivative Liability, Fair Value, Gross	0	0
Not designated as hedges | Mortgage banking | Interest rate contracts | Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	435	603
Derivative Asset, Fair Value, Gross	0	2
Derivative Liability, Fair Value, Gross	0	0
Not designated as hedges | Mortgage banking | Interest rate contracts | Interest rate lock commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	9,682	4,427
Derivative Asset, Fair Value, Gross	214	34
Derivative Liability, Fair Value, Gross	0	(2)
Not designated as hedges | Mortgage banking | Interest rate contracts | When issued securities, forward rate agreements and forward commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	13,287	11,997
Derivative Asset, Fair Value, Gross	4	10
Derivative Liability, Fair Value, Gross	(86)	(18)
Not designated as hedges | MSRs | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	21,923	26,842
Derivative Asset, Fair Value, Gross	19	24
Derivative Liability, Fair Value, Gross	0	(7)
Not designated as hedges | MSRs | Interest rate contracts | Swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	19,549	19,196
Derivative Asset, Fair Value, Gross	0	0
Derivative Liability, Fair Value, Gross	0	0
Not designated as hedges | MSRs | Interest rate contracts | Options
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	262	1,519
Derivative Asset, Fair Value, Gross	6	22
Derivative Liability, Fair Value, Gross	0	(2)
Not designated as hedges | MSRs | Interest rate contracts | Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	671	567
Derivative Asset, Fair Value, Gross	0	0
Derivative Liability, Fair Value, Gross	0	0
Not designated as hedges | MSRs | Interest rate contracts | When issued securities, forward rate agreements and forward commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	1,441	5,560
Derivative Asset, Fair Value, Gross	13	2
Derivative Liability, Fair Value, Gross	$ 0	$ (5)