Loans, Leases, and Allowance for Credit Losses (Summary of Past Due Loans (Accruing and Nonaccruing)) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	$ 57,779	$ 55,653
Accruing loans 90+ days past due	3	6
Nonaccrual loans that are current	222	149
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	30,588	30,495
Accruing loans 90+ days past due	2	5
Nonaccrual loans that are current	104	87
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	13,371	12,739
Accruing loans 90+ days past due	0	0
Nonaccrual loans that are current	61	14
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	13,820	12,419
Accruing loans 90+ days past due	1	1
Nonaccrual loans that are current	57	48
Commercial and industrial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	16,684	16,377
Accruing loans 90+ days past due	1	4
Nonaccrual loans that are current	82	63
Leasing | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	383	386
Accruing loans 90+ days past due	0	0
Nonaccrual loans that are current	2
Owner-occupied | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	9,219	9,371
Accruing loans 90+ days past due	1	1
Nonaccrual loans that are current	20	24
Municipal | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	4,302	4,361
Accruing loans 90+ days past due	0	0
Construction and land development | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	2,669	2,513
Accruing loans 90+ days past due	0	0
Nonaccrual loans that are current	22
Term | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	10,702	10,226
Accruing loans 90+ days past due	0	0
Nonaccrual loans that are current	39	14
Home equity credit line | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	3,356	3,377
Accruing loans 90+ days past due	0	0
Nonaccrual loans that are current	17	11
1-4 family residential | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	8,415	7,286
Accruing loans 90+ days past due	0	0
Nonaccrual loans that are current	40	37
Construction and other consumer real estate | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	1,442	1,161
Accruing loans 90+ days past due		0
Bankcard and other revolving plans | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	474	471
Accruing loans 90+ days past due	1	1
Other | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	133	124
Accruing loans 90+ days past due	0	0
Current
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	57,576	55,491
Current | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	30,519	30,422
Current | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	13,306	12,690
Current | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	13,751	12,379
Current | Commercial and industrial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	16,631	16,331
Current | Leasing | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	381	386
Current | Owner-occupied | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	9,206	9,344
Current | Municipal | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	4,301	4,361
Current | Construction and land development | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	2,645	2,511
Current | Term | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	10,661	10,179
Current | Home equity credit line | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	3,334	3,369
Current | 1-4 family residential | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	8,375	7,258
Current | Construction and other consumer real estate | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	1,442	1,161
Current | Bankcard and other revolving plans | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	468	467
Current | Other | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	132	124
Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	203	162
Total past due | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	69	73
Total past due | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	65	49
Total past due | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	69	40
Total past due | Commercial and industrial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	53	46
Total past due | Leasing | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	2	0
Total past due | Owner-occupied | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	13	27
Total past due | Municipal | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	1	0
Total past due | Construction and land development | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	24	2
Total past due | Term | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	41	47
Total past due | Home equity credit line | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	22	8
Total past due | 1-4 family residential | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	40	28
Total past due | Construction and other consumer real estate | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	0	0
Total past due | Bankcard and other revolving plans | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	6	4
Total past due | Other | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	1	0
30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	108	100
30-89 days past due | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	52	44
30-89 days past due | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	16	39
30-89 days past due | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	40	17
30-89 days past due | Commercial and industrial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	38	24
30-89 days past due | Leasing | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	2	0
30-89 days past due | Owner-occupied | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	11	20
30-89 days past due | Municipal | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	1	0
30-89 days past due | Construction and land development | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	2	2
30-89 days past due | Term | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	14	37
30-89 days past due | Home equity credit line | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	17	5
30-89 days past due | 1-4 family residential | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	17	9
30-89 days past due | Construction and other consumer real estate | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	0	0
30-89 days past due | Bankcard and other revolving plans | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	5	3
30-89 days past due | Other | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	1	0
90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	95	62
90+ days past due | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	17	29
90+ days past due | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	49	10
90+ days past due | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	29	23
90+ days past due | Commercial and industrial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	15	22
90+ days past due | Leasing | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	0	0
90+ days past due | Owner-occupied | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	2	7
90+ days past due | Municipal | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	0	0
90+ days past due | Construction and land development | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	22	0
90+ days past due | Term | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	27	10
90+ days past due | Home equity credit line | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	5	3
90+ days past due | 1-4 family residential | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	23	19
90+ days past due | Construction and other consumer real estate | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	0	0
90+ days past due | Bankcard and other revolving plans | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	1	1
90+ days past due | Other | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	0	0
Nonaccrual loans that are current
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	108	86
Nonaccrual loans that are current | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	83	60
Nonaccrual loans that are current | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	3	4
Nonaccrual loans that are current | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	22	22
Nonaccrual loans that are current | Commercial and industrial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	65	45
Nonaccrual loans that are current | Leasing | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	0	0
Nonaccrual loans that are current | Owner-occupied | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	18	15
Nonaccrual loans that are current | Municipal | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	0	0
Nonaccrual loans that are current | Construction and land development | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	0	0
Nonaccrual loans that are current | Term | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	3	4
Nonaccrual loans that are current | Home equity credit line | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	9	6
Nonaccrual loans that are current | 1-4 family residential | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	13	16
Nonaccrual loans that are current | Construction and other consumer real estate | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	0	0
Nonaccrual loans that are current | Bankcard and other revolving plans | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	0	0
Nonaccrual loans that are current | Other | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	$ 0	$ 0