Derivative Financial Instruments - Schedule of Derivative Financial Instruments and Related Hedged Items (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Hedge ineffectiveness	The ineffective portion was immaterial for all periods presented.
Notional Amount	$ 75,172	$ 78,277
Fair Value, Gain	443	822
Fair Value, Loss	(714)	(1,003)
Gross amounts not offset in the Consolidated Balance Sheets: Fair Value, Gain
Amounts subject to master netting arrangements not offset due to policy election	(297)	(443)
Cash collateral (received) posted	(20)	(119)
Net amount	126	260
Gross amounts not offset in the Consolidated Balance Sheets: Fair Value, Loss
Amounts subject to master netting arrangements not offset due to policy election	297	443
Cash collateral (received) posted	344	450
Net amount	(73)	(110)
Not designated as hedges
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	46,400	55,761
Fair Value, Gain	320	616
Fair Value, Loss	(344)	(630)
Cash flow hedges \| Interest rate contracts \| Pay fixed swaps \| 3 mo. LIBOR funding
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	6,500	7,050
Fair Value, Gain	0	0
Fair Value, Loss	(126)	(187)
Fair value hedges \| Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	22,272	15,466
Fair Value, Gain	123	206
Fair Value, Loss	(244)	(186)
Fair value hedges \| Interest rate contracts \| Pay fixed swaps \| Commercial loans
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	416	346
Fair Value, Gain	5	4
Fair Value, Loss	(1)	(2)
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	(76)	(83)
Fair value hedges \| Interest rate contracts \| Receive fixed swaps \| Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	15,538	12,099
Fair Value, Gain	118	202
Fair Value, Loss	(166)	(100)
Fair value hedges \| Interest rate contracts \| Options \| Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	6,087	2,790
Fair Value, Gain	0	0
Fair Value, Loss	(1)	(1)
Client-related and other risk management \| Not designated as hedges
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	27,519	28,688
Fair Value, Gain	210	319
Fair Value, Loss	(228)	(336)
Client-related and other risk management \| Not designated as hedges \| Interest rate contracts \| Pay fixed swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	10,962	10,263
Fair Value, Gain	59	43
Fair Value, Loss	(155)	(252)
Client-related and other risk management \| Not designated as hedges \| Interest rate contracts \| Receive fixed swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	10,880	9,989
Fair Value, Gain	141	235
Fair Value, Loss	(61)	(44)
Client-related and other risk management \| Not designated as hedges \| Interest rate contracts \| Other swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	936	1,086
Fair Value, Gain	2	2
Fair Value, Loss	(2)	(5)
Client-related and other risk management \| Not designated as hedges \| Interest rate contracts \| Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	722	709
Fair Value, Gain	2	2
Fair Value, Loss	(2)	(2)
Client-related and other risk management \| Not designated as hedges \| Interest rate contracts \| Forward commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	3,549	5,972
Fair Value, Gain	3	29
Fair Value, Loss	(2)	(28)
Client-related and other risk management \| Not designated as hedges \| Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	470	669
Fair Value, Gain	3	8
Fair Value, Loss	(6)	(5)
Mortgage banking \| Not designated as hedges \| Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	4,614	9,351
Fair Value, Gain	12	60
Fair Value, Loss	(6)	(35)
Mortgage banking \| Not designated as hedges \| Interest rate contracts \| Interest rate lock commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	1,308	2,219
Fair Value, Gain	7	7
Fair Value, Loss	(3)	(20)
Mortgage banking \| Not designated as hedges \| Interest rate contracts \| When issued securities, forward rate agreements and forward commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	3,124	6,683
Fair Value, Gain	4	51
Fair Value, Loss	(3)	(14)
Mortgage banking \| Not designated as hedges \| Interest rate contracts \| Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	182	449
Fair Value, Gain	1	2
Fair Value, Loss	0	(1)
MSRs \| Not designated as hedges \| Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	14,267	17,722
Fair Value, Gain	98	237
Fair Value, Loss	(110)	(259)
MSRs \| Not designated as hedges \| Interest rate contracts \| Pay fixed swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	3,418	3,768
Fair Value, Gain	32	56
Fair Value, Loss	(13)	(7)
MSRs \| Not designated as hedges \| Interest rate contracts \| Receive fixed swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	4,498	5,034
Fair Value, Gain	15	18
Fair Value, Loss	(86)	(236)
MSRs \| Not designated as hedges \| Interest rate contracts \| Options
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	4,535	5,710
Fair Value, Gain	50	160
Fair Value, Loss	(11)	(8)
MSRs \| Not designated as hedges \| Interest rate contracts \| When issued securities, forward rate agreements and forward commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	1,813	3,210
Fair Value, Gain	1	3
Fair Value, Loss	0	(8)
MSRs \| Not designated as hedges \| Interest rate contracts \| Other
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	3	0
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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