Fair Value of Assets and Liabilities - Schedule of Book Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Assets:
Net loans and leases	$ 62,281	$ 61,750
Short-term financial assets:
Interest-bearing deposits with banks	1,228	1,538
Securities purchased under agreements to resell	679	572
Trading securities	2,070	1,387
Loans held for sale:	501	551
Securities available for sale at fair value	8,102	7,896
Securities held to maturity	1,229	1,270
Derivative assets	352	530
Other assets:
Total assets	83,192	82,152
Liabilities:
Trading liabilities	662	550
Short-term financial liabilities:
Securities sold under agreements to repurchase	1,866	2,096
Term borrowings:
Other long-term borrowings	1,328	1,195
Derivative liabilities	401	655
Total liabilities	73,948	73,041
Level 3 | FHLB-Cincinnati Stock
Term borrowings:
Restricted investments	91	51
Level 3 | FRB Stock
Term borrowings:
Restricted investments	203	203
Reported Value Measurement
Assets:
Net loans and leases	62,281	61,750
Short-term financial assets:
Interest-bearing deposits with banks	1,228	1,538
Federal funds sold	95	59
Securities purchased under agreements to resell	679	572
Total short-term financial assets	2,002	2,169
Trading securities	2,070	1,387
Loans held for sale:	501	551
Securities available for sale at fair value	8,102	7,896
Securities held to maturity	1,229	1,270
Derivative assets	352	531
Other assets:
Tax credit investments	785	706
Deferred compensation mutual funds	112	111
Equity, mutual funds, and other	330	289
Total other assets	1,227	1,106
Total assets	77,764	76,660
Liabilities:
Defined maturity deposits	6,201	6,613
Trading liabilities	662	550
Short-term financial liabilities:
Federal funds purchased	809	259
Securities sold under agreements to repurchase	1,866	2,096
Other short-term borrowings	1,596	1,045
Total short-term financial liabilities	4,271	3,400
Term borrowings:
Real estate investment trust-preferred	47	47
Notes payable—new market tax credit investments	81	74
Secured borrowings	13	37
Junior subordinated debentures	152	151
Other long-term borrowings	1,035	886
Total term borrowings	1,328	1,195
Derivative liabilities	424	671
Total liabilities	12,886	12,429
Reported Value Measurement | Commercial, financial, and industrial
Assets:
Net loans and leases	34,067	33,083
Reported Value Measurement | Commercial Real Estate
Assets:
Net loans and leases	13,471	14,194
Reported Value Measurement | Consumer Real Estate
Assets:
Net loans and leases	14,184	13,826
Reported Value Measurement | Credit card and other
Assets:
Net loans and leases	559	647
Reported Value Measurement | Mortgage loans (elected fair value)
Short-term financial assets:
Loans held for sale:	139	85
Reported Value Measurement | USDA & SBA loans - LOCOM
Short-term financial assets:
Loans held for sale:	339	439
Reported Value Measurement | Mortgage loans - LOCOM
Short-term financial assets:
Loans held for sale:	23	27
Estimate of Fair Value Measurement
Assets:
Net loans and leases	61,343	60,324
Short-term financial assets:
Interest-bearing deposits with banks	1,228	1,538
Federal funds sold	95	59
Securities purchased under agreements to resell	679	572
Total short-term financial assets	2,002	2,169
Trading securities	2,070	1,387
Loans held for sale:	501	551
Securities available for sale at fair value	8,102	7,896
Securities held to maturity	1,079	1,083
Derivative assets	352	531
Other assets:
Tax credit investments	734	692
Deferred compensation mutual funds	112	111
Equity, mutual funds, and other	330	289
Total other assets	1,176	1,092
Total assets	76,625	75,033
Liabilities:
Defined maturity deposits	6,184	6,591
Trading liabilities	662	550
Short-term financial liabilities:
Federal funds purchased	809	259
Securities sold under agreements to repurchase	1,866	2,096
Other short-term borrowings	1,596	1,045
Total short-term financial liabilities	4,271	3,400
Term borrowings:
Real estate investment trust-preferred	47	47
Notes payable—new market tax credit investments	80	70
Secured borrowings	13	37
Junior subordinated debentures	142	142
Other long-term borrowings	1,050	866
Total term borrowings	1,332	1,162
Derivative liabilities	424	671
Total liabilities	12,873	12,374
Unfunded Commitments [Abstract]
Loan commitments	1	1
Standby and other commitments	11	9
Estimate of Fair Value Measurement | Level 1
Assets:
Net loans and leases	0	0
Short-term financial assets:
Interest-bearing deposits with banks	1,228	1,538
Federal funds sold	0	0
Securities purchased under agreements to resell	0	0
Total short-term financial assets	1,228	1,538
Trading securities	0	0
Loans held for sale:	0	0
Securities available for sale at fair value	0	0
Securities held to maturity	0	0
Derivative assets	9	8
Other assets:
Tax credit investments	0	0
Deferred compensation mutual funds	112	111
Equity, mutual funds, and other	36	35
Total other assets	148	146
Total assets	1,385	1,692
Liabilities:
Defined maturity deposits	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
Total short-term financial liabilities	0	0
Term borrowings:
Real estate investment trust-preferred	0	0
Notes payable—new market tax credit investments	0	0
Secured borrowings	0	0
Junior subordinated debentures	0	0
Other long-term borrowings	0	0
Total term borrowings	0	0
Derivative liabilities	8	6
Total liabilities	8	6
Estimate of Fair Value Measurement | Level 2
Assets:
Net loans and leases	0	0
Short-term financial assets:
Interest-bearing deposits with banks	0	0
Federal funds sold	95	59
Securities purchased under agreements to resell	679	572
Total short-term financial assets	774	631
Trading securities	2,044	1,364
Loans held for sale:	465	508
Securities available for sale at fair value	8,102	7,896
Securities held to maturity	1,079	1,083
Derivative assets	343	523
Other assets:
Tax credit investments	0	0
Deferred compensation mutual funds	0	0
Equity, mutual funds, and other	0	0
Total other assets	0	0
Total assets	12,807	12,005
Liabilities:
Defined maturity deposits	6,184	6,591
Trading liabilities	662	550
Short-term financial liabilities:
Federal funds purchased	809	259
Securities sold under agreements to repurchase	1,866	2,096
Other short-term borrowings	1,596	1,045
Total short-term financial liabilities	4,271	3,400
Term borrowings:
Real estate investment trust-preferred	0	0
Notes payable—new market tax credit investments	0	0
Secured borrowings	0	0
Junior subordinated debentures	0	0
Other long-term borrowings	1,050	866
Total term borrowings	1,050	866
Derivative liabilities	394	650
Total liabilities	12,561	12,057
Estimate of Fair Value Measurement | Level 3
Assets:
Net loans and leases	61,343	60,324
Short-term financial assets:
Interest-bearing deposits with banks	0	0
Federal funds sold	0	0
Securities purchased under agreements to resell	0	0
Total short-term financial assets	0	0
Trading securities	26	23
Loans held for sale:	36	43
Securities available for sale at fair value	0	0
Securities held to maturity	0	0
Derivative assets	0	0
Other assets:
Tax credit investments	734	692
Deferred compensation mutual funds	0	0
Equity, mutual funds, and other	294	254
Total other assets	1,028	946
Total assets	62,433	61,336
Liabilities:
Defined maturity deposits	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
Total short-term financial liabilities	0	0
Term borrowings:
Real estate investment trust-preferred	47	47
Notes payable—new market tax credit investments	80	70
Secured borrowings	13	37
Junior subordinated debentures	142	142
Other long-term borrowings	0	0
Total term borrowings	282	296
Derivative liabilities	22	15
Total liabilities	304	311
Estimate of Fair Value Measurement | Commercial, financial, and industrial
Assets:
Net loans and leases	33,590	32,511
Estimate of Fair Value Measurement | Commercial, financial, and industrial | Level 1
Assets:
Net loans and leases	0	0
Estimate of Fair Value Measurement | Commercial, financial, and industrial | Level 2
Assets:
Net loans and leases	0	0
Estimate of Fair Value Measurement | Commercial, financial, and industrial | Level 3
Assets:
Net loans and leases	33,590	32,511
Estimate of Fair Value Measurement | Commercial Real Estate
Assets:
Net loans and leases	13,409	13,894
Estimate of Fair Value Measurement | Commercial Real Estate | Level 1
Assets:
Net loans and leases	0	0
Estimate of Fair Value Measurement | Commercial Real Estate | Level 2
Assets:
Net loans and leases	0	0
Estimate of Fair Value Measurement | Commercial Real Estate | Level 3
Assets:
Net loans and leases	13,409	13,894
Estimate of Fair Value Measurement | Consumer Real Estate
Assets:
Net loans and leases	13,766	13,262
Estimate of Fair Value Measurement | Consumer Real Estate | Level 1
Assets:
Net loans and leases	0	0
Estimate of Fair Value Measurement | Consumer Real Estate | Level 2
Assets:
Net loans and leases	0	0
Estimate of Fair Value Measurement | Consumer Real Estate | Level 3
Assets:
Net loans and leases	13,766	13,262
Estimate of Fair Value Measurement | Credit card and other
Assets:
Net loans and leases	578	657
Estimate of Fair Value Measurement | Credit card and other | Level 1
Assets:
Net loans and leases	0	0
Estimate of Fair Value Measurement | Credit card and other | Level 2
Assets:
Net loans and leases	0	0
Estimate of Fair Value Measurement | Credit card and other | Level 3
Assets:
Net loans and leases	578	657
Estimate of Fair Value Measurement | Mortgage loans (elected fair value)
Short-term financial assets:
Loans held for sale:	139	85
Estimate of Fair Value Measurement | Mortgage loans (elected fair value) | Level 1
Short-term financial assets:
Loans held for sale:	0	0
Estimate of Fair Value Measurement | Mortgage loans (elected fair value) | Level 2
Short-term financial assets:
Loans held for sale:	126	69
Estimate of Fair Value Measurement | Mortgage loans (elected fair value) | Level 3
Short-term financial assets:
Loans held for sale:	13	16
Estimate of Fair Value Measurement | USDA & SBA loans - LOCOM
Short-term financial assets:
Loans held for sale:	339	439
Estimate of Fair Value Measurement | USDA & SBA loans - LOCOM | Level 1
Short-term financial assets:
Loans held for sale:	0	0
Estimate of Fair Value Measurement | USDA & SBA loans - LOCOM | Level 2
Short-term financial assets:
Loans held for sale:	339	439
Estimate of Fair Value Measurement | USDA & SBA loans - LOCOM | Level 3
Short-term financial assets:
Loans held for sale:	0	0
Estimate of Fair Value Measurement | Mortgage loans - LOCOM
Short-term financial assets:
Loans held for sale:	23	27
Estimate of Fair Value Measurement | Mortgage loans - LOCOM | Level 1
Short-term financial assets:
Loans held for sale:	0	0
Estimate of Fair Value Measurement | Mortgage loans - LOCOM | Level 2
Short-term financial assets:
Loans held for sale:	0	0
Estimate of Fair Value Measurement | Mortgage loans - LOCOM | Level 3
Short-term financial assets:
Loans held for sale:	23	27
Contractual Amount
Unfunded Commitments [Abstract]
Loan commitments	21,551	20,992
Standby and other commitments	$ 788	$ 753