Derivative Financial Instruments - Classifications and Hedging Relationships (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	$ 78,649	$ 75,172
Fair Value, Gain	199	443
Fair Value, Loss	(412)	(714)
Derivative Asset [Abstract]
Amounts subject to master netting arrangements not offset due to policy election	(81)	(297)
Cash collateral (received) posted	(39)	(20)
Net amount	79	126
Derivative Liability [Abstract]
Amounts subject to master netting arrangements not offset due to policy election	81	297
Cash collateral (received) posted	162	344
Net amount	(169)	(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	22,281	22,272
Fair Value, Gain	3	123
Fair Value, Loss	(186)	(244)
Fair value hedges \| Interest rate contracts \| Pay fixed swaps \| Commercial loans
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	392	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	231	231
Fair Value, Gain	0	0
Fair Value, Loss	(55)	(76)
Fair value hedges \| Interest rate contracts \| Receive fixed swaps \| Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	15,571	15,538
Fair Value, Gain	1	118
Fair Value, Loss	(130)	(166)
Fair value hedges \| Interest rate contracts \| Options \| Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	6,087	6,087
Fair Value, Gain	0	0
Fair Value, Loss	(1)	(1)
Not designated as hedges
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	49,868	46,400
Fair Value, Gain	196	320
Fair Value, Loss	(226)	(344)
Not designated as hedges \| Client-related and other risk management
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	28,177	27,519
Fair Value, Gain	102	210
Fair Value, Loss	(203)	(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	11,033	10,962
Fair Value, Gain	27	59
Fair Value, Loss	(40)	(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	10,800	10,880
Fair Value, Gain	61	141
Fair Value, Loss	(150)	(61)
Not designated as hedges \| Client-related and other risk management \| Interest rate contracts \| Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	1,722	1,658
Fair Value, Gain	3	4
Fair Value, Loss	(4)	(4)
Not designated as hedges \| Client-related and other risk management \| Interest rate contracts \| Forward commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	4,116	3,549
Fair Value, Gain	8	3
Fair Value, Loss	(6)	(2)
Not designated as hedges \| Client-related and other risk management \| Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	506	470
Fair Value, Gain	3	3
Fair Value, Loss	(3)	(6)
Not designated as hedges \| Mortgage banking \| Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	5,479	4,614
Fair Value, Gain	22	12
Fair Value, Loss	(12)	(6)
Not designated as hedges \| Mortgage banking \| Interest rate contracts \| Interest rate lock commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	1,641	1,308
Fair Value, Gain	11	7
Fair Value, Loss	(4)	(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	3,502	3,124
Fair Value, Gain	9	4
Fair Value, Loss	(8)	(3)
Not designated as hedges \| Mortgage banking \| Interest rate contracts \| Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	336	182
Fair Value, Gain	2	1
Fair Value, Loss	0	0
Not designated as hedges \| MSRs \| Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	16,212	14,267
Fair Value, Gain	72	98
Fair Value, Loss	(11)	(110)
Not designated as hedges \| MSRs \| Interest rate contracts \| Pay fixed swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	5,226	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	5,599	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	4,275	4,535
Fair Value, Gain	67	50
Fair Value, Loss	(11)	(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	1,077	1,813
Fair Value, Gain	5	1
Fair Value, Loss	0	0
Not designated as hedges \| MSRs \| Interest rate contracts \| Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	35	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
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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