Derivative Financial Instruments - Classifications and Hedging Relationships (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	$ 72,998	$ 67,738
Fair Value, Gain	338	246
Fair Value, Loss	(180)	(247)
Derivative Asset [Abstract]
Amounts subject to master netting arrangements not offset due to policy election	(44)	(47)
Cash collateral (received) posted	(50)	(53)
Net amount	244	146
Derivative Liability [Abstract]
Amounts subject to master netting arrangements not offset due to policy election	44	47
Cash collateral (received) posted	64	82
Net amount	(72)	(118)
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	0
Fair value hedges \| Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	18,572	18,457
Fair Value, Gain	41	7
Fair Value, Loss	(56)	(76)
Fair value hedges \| Interest rate contracts \| Pay fixed swaps \| Commercial loans
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	499	505
Fair Value, Gain	1	2
Fair Value, Loss	0	0
Fair value hedges \| Interest rate contracts \| Pay fixed swaps \| Municipal securities
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	259	259
Fair Value, Gain	0	0
Fair Value, Loss	0	0
Fair value hedges \| Interest rate contracts \| Receive fixed swaps \| Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	13,029	12,908
Fair Value, Gain	40	5
Fair Value, Loss	(54)	(74)
Fair value hedges \| Interest rate contracts \| Options \| Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	4,785	4,785
Fair Value, Gain	0	0
Fair Value, Loss	(2)	(2)
Not designated as hedges
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	47,926	42,781
Fair Value, Gain	297	239
Fair Value, Loss	(124)	(171)
Not designated as hedges \| Client-related and other risk management
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	31,220	27,655
Fair Value, Gain	253	165
Fair Value, Loss	(104)	(148)
Not designated as hedges \| Client-related and other risk management \| Interest rate contracts \| Pay fixed swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	11,774	11,523
Fair Value, Gain	9	19
Fair Value, Loss	(43)	(32)
Not designated as hedges \| Client-related and other risk management \| Interest rate contracts \| Receive fixed swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	12,452	11,577
Fair Value, Gain	228	128
Fair Value, Loss	(46)	(98)
Not designated as hedges \| Client-related and other risk management \| Interest rate contracts \| Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	1,384	1,143
Fair Value, Gain	1	2
Fair Value, Loss	(2)	(3)
Not designated as hedges \| Client-related and other risk management \| Interest rate contracts \| Forward commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	5,042	2,883
Fair Value, Gain	12	11
Fair Value, Loss	(11)	(13)
Not designated as hedges \| Client-related and other risk management \| Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	568	529
Fair Value, Gain	3	5
Fair Value, Loss	(2)	(2)
Not designated as hedges \| Mortgage banking \| Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	3,604	2,726
Fair Value, Gain	12	16
Fair Value, Loss	(18)	(21)
Not designated as hedges \| Mortgage banking \| Interest rate contracts \| Interest rate lock commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	1,092	702
Fair Value, Gain	10	12
Fair Value, Loss	(3)	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	2,314	1,753
Fair Value, Gain	1	2
Fair Value, Loss	(15)	(20)
Not designated as hedges \| Mortgage banking \| Interest rate contracts \| Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	198	271
Fair Value, Gain	1	2
Fair Value, Loss	0	(1)
Not designated as hedges \| MSRs \| Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	13,102	12,400
Fair Value, Gain	32	58
Fair Value, Loss	(2)	(2)
Not designated as hedges \| MSRs \| Interest rate contracts \| Pay fixed swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	3,822	3,224
Fair Value, Gain	0	0
Fair Value, Loss	(1)	0
Not designated as hedges \| MSRs \| Interest rate contracts \| Receive fixed swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	4,629	4,328
Fair Value, Gain	1	0
Fair Value, Loss	0	0
Not designated as hedges \| MSRs \| Interest rate contracts \| Options
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	2,080	3,155
Fair Value, Gain	25	48
Fair Value, Loss	0	(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	2,517	1,590
Fair Value, Gain	6	10
Fair Value, Loss	(1)	0
Not designated as hedges \| MSRs \| Interest rate contracts \| Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	54	103
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
-Publisher SEC
-Name Regulation S-X (SX)
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