Derivative Financial Instruments - Classifications and Hedging Relationships (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	$ 315,873	$ 67,738
Fair Value, Gain	4,260	246
Fair Value, Loss	(3,336)	(247)
Derivative Asset [Abstract]
Amounts subject to master netting arrangements	(1,708)
Amounts subject to master netting arrangements		(47)
Cash collateral (received) posted for amounts subject to master netting arrangements	(499)
Cash collateral (received) posted for amounts subject to master netting arrangements		(53)
Net amount	2,053	146
Derivative Liability [Abstract]
Amounts subject to master netting arrangements	1,708
Amounts subject to master netting arrangements not offset due to policy election		47
Cash collateral (received) posted for amounts subject to master netting arrangements	1,262
Cash collateral (received) posted for amounts subject to master netting arrangements		82
Net amount	(366)	(118)
Derivatives Subject to Master Netting Arrangements
Derivative Instruments, Gain (Loss) [Line Items]
Fair Value, Gain	3,516
Fair Value, Loss	(2,939)
Derivative Asset [Abstract]
Net amount	(1,513)
Derivative Liability [Abstract]
Net amount	(178)
Cash flow hedges | Interest rate contracts | Swap | 3 mo. LIBOR funding
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	0	6,500
Fair Value, Gain	0	0
Fair Value, Loss	0	0
Fair value hedges | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	27,152	18,457
Fair Value, Gain	113	7
Fair Value, Loss	(27)	(76)
Fair value hedges | Interest rate contracts | Options | Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	3,407	4,785
Fair Value, Gain	0	0
Fair Value, Loss	(2)	(2)
Fair value hedges | Interest rate contracts | Swap | Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	23,701	12,908
Fair Value, Gain	113	5
Fair Value, Loss	(25)	(74)
Fair value hedges | Interest rate contracts | Swap | Commercial loans
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	44	505
Fair Value, Gain	0	2
Fair Value, Loss	0	0
Fair value hedges | Interest rate contracts | Swap | Municipal securities
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	0	259
Fair Value, Gain	0	0
Fair Value, Loss	0	0
Not designated as hedges
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	288,721	42,781
Fair Value, Gain	4,147	239
Fair Value, Loss	(3,309)	(171)
Not designated as hedges | Client-related and other risk management
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	244,317	27,655
Fair Value, Gain	4,077	165
Fair Value, Loss	(3,282)	(148)
Not designated as hedges | Client-related and other risk management | Interest rate contracts | Options
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	25,938	491
Fair Value, Gain	28	1
Fair Value, Loss	(19)	(1)
Not designated as hedges | Client-related and other risk management | Interest rate contracts | Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	1,807	4
Fair Value, Gain	0	0
Fair Value, Loss	0	0
Not designated as hedges | Client-related and other risk management | Interest rate contracts | Forward commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	7,907	2,883
Fair Value, Gain	6	11
Fair Value, Loss	(7)	(13)
Not designated as hedges | Client-related and other risk management | Interest rate contracts | Swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	144,473	23,302
Fair Value, Gain	1,817	148
Fair Value, Loss	(673)	(132)
Not designated as hedges | Client-related and other risk management | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	12,986	529
Fair Value, Gain	144	5
Fair Value, Loss	(164)	(2)
Not designated as hedges | Client-related and other risk management | Equity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	38,426	0
Fair Value, Gain	1,988	0
Fair Value, Loss	(2,307)	0
Not designated as hedges | Client-related and other risk management | Credit Contract | Loans and leases
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	894	0
Fair Value, Gain	0	0
Fair Value, Loss	(34)	0
Not designated as hedges | Client-related and other risk management | Credit Contract | Risk participation agreements
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	6,696	446
Fair Value, Gain	0	0
Fair Value, Loss	(2)	0
Not designated as hedges | Client-related and other risk management | Credit Contract | Total Return Swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	2,531	0
Fair Value, Gain	27	0
Fair Value, Loss	(11)	0
Not designated as hedges | Client-related and other risk management | Commodity Contract
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	2,659	0
Fair Value, Gain	67	0
Fair Value, Loss	(65)	0
Not designated as hedges | Mortgage banking | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	17,562	2,726
Fair Value, Gain	46	16
Fair Value, Loss	(20)	(21)
Not designated as hedges | Mortgage banking | Interest rate contracts | Interest rate lock commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	4,427	702
Fair Value, Gain	34	12
Fair Value, Loss	(2)	0
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	11,997	1,753
Fair Value, Gain	10	2
Fair Value, Loss	(18)	(20)
Not designated as hedges | Mortgage banking | Interest rate contracts | Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	603	128
Fair Value, Gain	2	2
Fair Value, Loss	0	(1)
Not designated as hedges | Mortgage banking | Interest rate contracts | Swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	535	143
Fair Value, Gain	0	0
Fair Value, Loss	0	0
Not designated as hedges | MSRs | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	26,842	12,400
Fair Value, Gain	24	58
Fair Value, Loss	(7)	(2)
Not designated as hedges | MSRs | Interest rate contracts | Options
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	1,519	3,155
Fair Value, Gain	22	48
Fair Value, Loss	(2)	(2)
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	5,560	1,590
Fair Value, Gain	2	10
Fair Value, Loss	(5)	0
Not designated as hedges | MSRs | Interest rate contracts | Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	567	103
Fair Value, Gain	0	0
Fair Value, Loss	0	0
Not designated as hedges | MSRs | Interest rate contracts | Swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	19,196	7,552
Fair Value, Gain	0	0
Fair Value, Loss	$ 0	$ 0