Fair Value of Assets and Liabilities - Summary Of Book Value And Estimated Fair Value Of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	$ 54,701	$ 57,269
Short-term financial assets:
Interest-bearing deposits with banks	14,829	8,351
Securities purchased under agreements to resell	355	380
Trading securities	1,319	1,176
Loans held for sale	1,052	1,022
Securities available for sale at fair value	8,494	8,047
Securities held to maturity (fair value of $303 and $10, respectively)	304	10
Derivative assets	451	765
Other assets:
Total assets	88,537	84,209
Liabilities:
Trading liabilities	315	353
Short-term financial liabilities:
Securities sold under agreements to repurchase	1,299	1,187
Term borrowings:
Other long term borrowings	1,584	1,670
Derivative liabilities	130	125
Total liabilities	80,005	75,902
Fair Value, Inputs, Level 3 | FHLB-Cincinnati Stock
Term borrowings:
Restricted investments	29	61
Fair Value, Inputs, Level 3 | FRB Stock
Term borrowings:
Restricted investments	203	202
Reported Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	54,701	57,269
Short-term financial assets:
Interest-bearing deposits with banks	14,829	8,351
Federal funds sold and securities purchased under agreements to resell	6	65
Securities purchased under agreements to resell	355	380
Total short-term financial assets	15,190	8,796
Trading securities	1,319	1,176
Loans held for sale	1,050	1,022
Securities available for sale at fair value	8,494	8,047
Securities held to maturity (fair value of $303 and $10, respectively)	304	10
Derivative assets	453	769
Other assets:
Tax credit investments	409	400
Deferred compensation assets	127	118
Equity, mutual funds, and other	260	288
Total other assets	796	806
Total assets	82,307	77,895
Liabilities:
Defined maturity	3,920	5,070
Trading liabilities	315	353
Short-term financial liabilities:
Federal funds purchased	814	845
Securities sold under agreements to repurchase	1,299	1,187
Other short-term borrowings	111	166
Short Term Financial Liabilities	2,224	2,198
Term borrowings:
Real estate investment trust-preferred	47	46
Term borrowings—new market tax credit investment	45	45
Secured borrowings	4	15
Junior subordinated debentures	160	238
Other long term borrowings	1,328	1,326
Total term borrowings	1,584	1,670
Derivative liabilities	147	149
Total liabilities	8,190	9,440
Reported Value Measurement | Commercial, financial and industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	31,142	32,651
Reported Value Measurement | Commercial Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	12,032	12,033
Reported Value Measurement | Consumer Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	10,608	11,483
Reported Value Measurement | Credit Card and Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	919	1,102
Reported Value Measurement | Mortgage loans (elected fair value)
Short-term financial assets:
Loans held for sale	301	405
Reported Value Measurement | Government guaranteed loans (SBA and USDA)
Short-term financial assets:
Loans held for sale	693	509
Reported Value Measurement | Other consumer loans- LOCOM
Short-term financial assets:
Loans held for sale	4	31
Reported Value Measurement | Mortgage loans - LOCOM
Short-term financial assets:
Loans held for sale	52	77
Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	55,095	57,695
Short-term financial assets:
Interest-bearing deposits with banks	14,829	8,351
Federal funds sold and securities purchased under agreements to resell	6	65
Securities purchased under agreements to resell	355	380
Total short-term financial assets	15,190	8,796
Trading securities	1,319	1,176
Loans held for sale	1,054	1,025
Securities available for sale at fair value	8,494	8,047
Securities held to maturity (fair value of $303 and $10, respectively)	303	10
Derivative assets	453	769
Other assets:
Tax credit investments	395	371
Deferred compensation assets	127	118
Equity, mutual funds, and other	260	288
Total other assets	782	777
Total assets	82,690	78,295
Liabilities:
Defined maturity	3,926	5,083
Trading liabilities	315	353
Short-term financial liabilities:
Federal funds purchased	814	845
Securities sold under agreements to repurchase	1,299	1,187
Other short-term borrowings	111	166
Short Term Financial Liabilities	2,224	2,198
Term borrowings:
Real estate investment trust-preferred	47	47
Term borrowings—new market tax credit investment	44	45
Secured borrowings	4	15
Junior subordinated debentures	184	223
Other long term borrowings	1,464	1,455
Total term borrowings	1,743	1,785
Derivative liabilities	147	149
Total liabilities	8,355	9,568
Unfunded Commitments:
Loan commitments	1	2
Standby and other commitments	8	6
Estimate of Fair Value Measurement | Commercial, financial and industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	30,972	32,582
Estimate of Fair Value Measurement | Commercial Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	12,027	12,079
Estimate of Fair Value Measurement | Consumer Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	11,151	11,903
Estimate of Fair Value Measurement | Credit Card and Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	945	1,131
Estimate of Fair Value Measurement | Mortgage loans (elected fair value)
Short-term financial assets:
Loans held for sale	301	405
Estimate of Fair Value Measurement | Government guaranteed loans (SBA and USDA)
Short-term financial assets:
Loans held for sale	697	512
Estimate of Fair Value Measurement | Other consumer loans- LOCOM
Short-term financial assets:
Loans held for sale	4	31
Estimate of Fair Value Measurement | Mortgage loans - LOCOM
Short-term financial assets:
Loans held for sale	52	77
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	0	0
Short-term financial assets:
Interest-bearing deposits with banks	14,829	8,351
Federal funds sold and securities purchased under agreements to resell	0	0
Securities purchased under agreements to resell	0	0
Total short-term financial assets	14,829	8,351
Trading securities	0	0
Loans held for sale	0	0
Securities available for sale at fair value	0	0
Securities held to maturity (fair value of $303 and $10, respectively)	0	0
Derivative assets	46	63
Other assets:
Tax credit investments	0	0
Deferred compensation assets	127	118
Equity, mutual funds, and other	28	25
Total other assets	155	143
Total assets	15,030	8,557
Liabilities:
Defined maturity	0	0
Trading liabilities	0	0
Short-term financial liabilities:
Federal funds purchased	0	0
Securities sold under agreements to repurchase	0	0
Other short-term borrowings	0	0
Short Term Financial Liabilities	0	0
Term borrowings:
Real estate investment trust-preferred	0	0
Term borrowings—new market tax credit investment	0	0
Secured borrowings	0	0
Junior subordinated debentures	0	0
Other long term borrowings	0	0
Total term borrowings	0	0
Derivative liabilities	35	71
Total liabilities	35	71
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 1 | Commercial, financial and industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	0	0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 1 | Commercial Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	0	0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 1 | Consumer Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	0	0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 1 | Credit Card and Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	0	0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 1 | Mortgage loans (elected fair value)
Short-term financial assets:
Loans held for sale	0	0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 1 | Government guaranteed loans (SBA and USDA)
Short-term financial assets:
Loans held for sale	0	0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 1 | Other consumer loans- LOCOM
Short-term financial assets:
Loans held for sale	0	0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 1 | Mortgage loans - LOCOM
Short-term financial assets:
Loans held for sale	0	0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	0	0
Short-term financial assets:
Interest-bearing deposits with banks	0	0
Federal funds sold and securities purchased under agreements to resell	6	65
Securities purchased under agreements to resell	355	380
Total short-term financial assets	361	445
Trading securities	1,319	1,176
Loans held for sale	977	935
Securities available for sale at fair value	8,478	8,015
Securities held to maturity (fair value of $303 and $10, respectively)	303	0
Derivative assets	407	706
Other assets:
Tax credit investments	0	0
Deferred compensation assets	0	0
Equity, mutual funds, and other	0	0
Total other assets	0	0
Total assets	11,845	11,277
Liabilities:
Defined maturity	3,926	5,083
Trading liabilities	315	353
Short-term financial liabilities:
Federal funds purchased	814	845
Securities sold under agreements to repurchase	1,299	1,187
Other short-term borrowings	111	166
Short Term Financial Liabilities	2,224	2,198
Term borrowings:
Real estate investment trust-preferred	0	0
Term borrowings—new market tax credit investment	0	0
Secured borrowings	0	0
Junior subordinated debentures	0	0
Other long term borrowings	1,464	1,455
Total term borrowings	1,464	1,455
Derivative liabilities	96	64
Total liabilities	8,025	9,153
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2 | Commercial, financial and industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	0	0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2 | Commercial Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	0	0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2 | Consumer Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	0	0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2 | Credit Card and Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	0	0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2 | Mortgage loans (elected fair value)
Short-term financial assets:
Loans held for sale	277	393
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2 | Government guaranteed loans (SBA and USDA)
Short-term financial assets:
Loans held for sale	696	511
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2 | Other consumer loans- LOCOM
Short-term financial assets:
Loans held for sale	4	31
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2 | Mortgage loans - LOCOM
Short-term financial assets:
Loans held for sale	0	0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	55,095	57,695
Short-term financial assets:
Interest-bearing deposits with banks	0	0
Federal funds sold and securities purchased under agreements to resell	0	0
Securities purchased under agreements to resell	0	0
Total short-term financial assets	0	0
Trading securities	0	0
Loans held for sale	77	90
Securities available for sale at fair value	16	32
Securities held to maturity (fair value of $303 and $10, respectively)	0	10
Derivative assets	0	0
Other assets:
Tax credit investments	395	371
Deferred compensation assets	0	0
Equity, mutual funds, and other	232	263
Total other assets	627	634
Total assets	55,815	58,461
Liabilities:
Defined maturity	0	0
Trading liabilities	0	0
Short-term financial liabilities:
Federal funds purchased	0	0
Securities sold under agreements to repurchase	0	0
Other short-term borrowings	0	0
Short Term Financial Liabilities	0	0
Term borrowings:
Real estate investment trust-preferred	47	47
Term borrowings—new market tax credit investment	44	45
Secured borrowings	4	15
Junior subordinated debentures	184	223
Other long term borrowings	0	0
Total term borrowings	279	330
Derivative liabilities	16	14
Total liabilities	295	344
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | Commercial, financial and industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	30,972	32,582
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | Commercial Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	12,027	12,079
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | Consumer Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	11,151	11,903
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | Credit Card and Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans and leases	945	1,131
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | Mortgage loans (elected fair value)
Short-term financial assets:
Loans held for sale	24	12
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | Government guaranteed loans (SBA and USDA)
Short-term financial assets:
Loans held for sale	1	1
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | Other consumer loans- LOCOM
Short-term financial assets:
Loans held for sale	0	0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | Mortgage loans - LOCOM
Short-term financial assets:
Loans held for sale	52	77
Contractual Amount
Unfunded Commitments:
Loan commitments	23,279	20,796
Standby and other commitments	$ 749	$ 751