Loans, Leases, and Allowance for Credit Losses (Summary of Past Due Loans (Accruing and Nonaccruing)) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	$ 50,851	$ 53,476
Accruing loans 90+ days past due	8	12
Nonaccrual loans that are current	271	367
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	28,440	30,472
Accruing loans 90+ days past due	7	2
Nonaccrual loans that are current	184	216
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	12,198	12,104
Accruing loans 90+ days past due	0	8
Nonaccrual loans that are current	20	31
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	10,213	10,900
Accruing loans 90+ days past due	1	2
Nonaccrual loans that are current	67	120
Commercial and industrial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	13,867	13,444
Accruing loans 90+ days past due	2	2
Nonaccrual loans that are current	124	140
PPP | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	1,855	5,572
Accruing loans 90+ days past due	5	0
Nonaccrual loans that are current	3
Leasing | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	327	320
Accruing loans 90+ days past due	0	0
Owner-occupied | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	8,733	8,185
Accruing loans 90+ days past due	0	0
Nonaccrual loans that are current	57	76
Municipal | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	3,658	2,951
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	2,757	2,345
Accruing loans 90+ days past due	0	4
Term | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	9,441	9,759
Accruing loans 90+ days past due	0	4
Nonaccrual loans that are current	20	31
Home equity credit line | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	3,016	2,745
Accruing loans 90+ days past due	0	0
Nonaccrual loans that are current	14	16
1-4 family residential | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	6,050	6,969
Accruing loans 90+ days past due	0	0
Nonaccrual loans that are current	52	103
Construction and other consumer real estate | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	638	630
Accruing loans 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	396	432
Accruing loans 90+ days past due	1	2
Nonaccrual loans that are current	1	1
Other | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	113	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	50,684	53,198
Current | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	28,332	30,360
Current | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	12,183	12,033
Current | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	10,169	10,805
Current | Commercial and industrial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	13,822	13,388
Current | PPP | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	1,813	5,572
Current | Leasing | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	327	320
Current | Owner-occupied | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	8,712	8,129
Current | Municipal | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	3,658	2,951
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	2,757	2,341
Current | Term | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	9,426	9,692
Current | Home equity credit line | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	3,008	2,733
Current | 1-4 family residential | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	6,018	6,891
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	638	630
Current | Bankcard and other revolving plans | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	393	428
Current | Other | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	112	123
Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	167	278
Total past due | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	108	112
Total past due | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	15	71
Total past due | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	44	95
Total past due | Commercial and industrial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	45	56
Total past due | PPP | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	42	0
Total past due | Leasing | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	0	0
Total past due | Owner-occupied | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	21	56
Total past due | Municipal | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	0	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	0	4
Total past due | Term | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	15	67
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	8	12
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	32	78
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	3	4
Total past due | Other | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	1	1
30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	82	140
30-89 days past due | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	59	60
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	10	57
30-89 days past due | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	13	23
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	17	26
30-89 days past due | PPP | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	35	0
30-89 days past due | Leasing | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	0	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	7	34
30-89 days past due | Municipal | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	0	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	0	0
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	10	57
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	4	8
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	6	12
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	2	2
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	1
90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	85	138
90+ days past due | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	49	52
90+ days past due | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	5	14
90+ days past due | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	31	72
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	28	30
90+ days past due | PPP | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and leases, net of unearned income and fees	7	0
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	14	22
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	0	4
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	5	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	4	4
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	26	66
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	2
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	182	214
Nonaccrual loans that are current | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	133	158
Nonaccrual loans that are current | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	15	13
Nonaccrual loans that are current | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	34	43
Nonaccrual loans that are current | Commercial and industrial | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	91	109
Nonaccrual loans that are current | PPP | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	0	0
Nonaccrual loans that are current | Leasing | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	0	1
Nonaccrual loans that are current | Owner-occupied | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	42	48
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	15	13
Nonaccrual loans that are current | Home equity credit line | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	10	9
Nonaccrual loans that are current | 1-4 family residential | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	24	33
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	1
Nonaccrual loans that are current | Other | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans that are current	$ 0	$ 0