Derivative Financial Instruments - Classifications and Hedging Relationships (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	$ 67,738	$ 75,172
Fair Value, Gain	246	443
Fair Value, Loss	(247)	(714)
Derivative Asset [Abstract]
Amounts subject to master netting arrangements not offset due to policy election	(47)	(297)
Cash collateral (received) posted	(53)	(20)
Net amount	146	126
Derivative Liability [Abstract]
Amounts subject to master netting arrangements not offset due to policy election	47	297
Cash collateral (received) posted	82	344
Net amount	(118)	(73)
Cash flow hedges \| Interest rate contracts \| Pay fixed swaps \| 3 mo. LIBOR funding
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	6,500	6,500
Fair Value, Gain	0	0
Fair Value, Loss	0	(126)
Fair value hedges \| Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	18,457	22,272
Fair Value, Gain	7	123
Fair Value, Loss	(76)	(244)
Fair value hedges \| Interest rate contracts \| Pay fixed swaps \| Commercial loans
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	505	416
Fair Value, Gain	2	5
Fair Value, Loss	0	(1)
Fair value hedges \| Interest rate contracts \| Pay fixed swaps \| Municipal securities
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	259	231
Fair Value, Gain	0	0
Fair Value, Loss	0	(76)
Fair value hedges \| Interest rate contracts \| Receive fixed swaps \| Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	12,908	15,538
Fair Value, Gain	5	118
Fair Value, Loss	(74)	(166)
Fair value hedges \| Interest rate contracts \| Options \| Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	4,785	6,087
Fair Value, Gain	0	0
Fair Value, Loss	(2)	(1)
Not designated as hedges
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	42,781	46,400
Fair Value, Gain	239	320
Fair Value, Loss	(171)	(344)
Not designated as hedges \| Client-related and other risk management
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	27,655	27,519
Fair Value, Gain	165	210
Fair Value, Loss	(148)	(228)
Not designated as hedges \| Client-related and other risk management \| Interest rate contracts \| Pay fixed swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	11,523	10,962
Fair Value, Gain	19	59
Fair Value, Loss	(32)	(155)
Not designated as hedges \| Client-related and other risk management \| Interest rate contracts \| Receive fixed swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	11,577	10,880
Fair Value, Gain	128	141
Fair Value, Loss	(98)	(61)
Not designated as hedges \| Client-related and other risk management \| Interest rate contracts \| Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	1,143	1,658
Fair Value, Gain	2	4
Fair Value, Loss	(3)	(4)
Not designated as hedges \| Client-related and other risk management \| Interest rate contracts \| Forward commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	2,883	3,549
Fair Value, Gain	11	3
Fair Value, Loss	(13)	(2)
Not designated as hedges \| Client-related and other risk management \| Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	529	470
Fair Value, Gain	5	3
Fair Value, Loss	(2)	(6)
Not designated as hedges \| Mortgage banking \| Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	2,726	4,614
Fair Value, Gain	16	12
Fair Value, Loss	(21)	(6)
Not designated as hedges \| Mortgage banking \| Interest rate contracts \| Interest rate lock commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	702	1,308
Fair Value, Gain	12	7
Fair Value, Loss	0	(3)
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	1,753	3,124
Fair Value, Gain	2	4
Fair Value, Loss	(20)	(3)
Not designated as hedges \| Mortgage banking \| Interest rate contracts \| Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	271	182
Fair Value, Gain	2	1
Fair Value, Loss	(1)	0
Not designated as hedges \| MSRs \| Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	12,400	14,267
Fair Value, Gain	58	98
Fair Value, Loss	(2)	(110)
Not designated as hedges \| MSRs \| Interest rate contracts \| Pay fixed swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	3,224	3,418
Fair Value, Gain	0	32
Fair Value, Loss	0	(13)
Not designated as hedges \| MSRs \| Interest rate contracts \| Receive fixed swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	4,328	4,498
Fair Value, Gain	0	15
Fair Value, Loss	0	(86)
Not designated as hedges \| MSRs \| Interest rate contracts \| Options
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	3,155	4,535
Fair Value, Gain	48	50
Fair Value, Loss	(2)	(11)
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	1,590	1,813
Fair Value, Gain	10	1
Fair Value, Loss	0	0
Not designated as hedges \| MSRs \| Interest rate contracts \| Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	103	3
Fair Value, Gain	0	0
Fair Value, Loss	$ 0	$ 0

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Regulation S-X (SX)
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