Loans and Leases - Age Analysis of Past Due Loans, by Class (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	$ 24,968	$ 25,459
90 Days Past Due and Still Accruing	6	16
Non- Accrual	88	170
Non-accrual with No ACL	24	52
30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	59	72
Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	153	258
Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	24,815	25,201
Total commercial loans and leases
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	16,465	17,470
90 Days Past Due and Still Accruing	0	0
Non- Accrual	64	132
Non-accrual with No ACL	24	52
Total commercial loans and leases | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	16	23
Total commercial loans and leases | Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	80	155
Total commercial loans and leases | Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	16,385	17,315
Total commercial loans and leases | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	9,899	9,731
90 Days Past Due and Still Accruing	0	0
Non- Accrual	48	85
Non-accrual with No ACL	20	36
Total commercial loans and leases | Commercial real estate | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	11	13
Total commercial loans and leases | Commercial real estate | Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	59	98
Total commercial loans and leases | Commercial real estate | Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	9,840	9,633
Total commercial loans and leases | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	5,977	7,214
90 Days Past Due and Still Accruing	0	0
Non- Accrual	15	44
Non-accrual with No ACL	4	16
Total commercial loans and leases | Commercial and industrial | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	4	8
Total commercial loans and leases | Commercial and industrial | Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	19	52
Total commercial loans and leases | Commercial and industrial | Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	5,958	7,162
Total commercial loans and leases | Commercial leases
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	495	485
90 Days Past Due and Still Accruing	0	0
Non- Accrual	1	2
Non-accrual with No ACL	0	0
Total commercial loans and leases | Commercial leases | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	1	2
Total commercial loans and leases | Commercial leases | Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	2	4
Total commercial loans and leases | Commercial leases | Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	493	481
Total commercial loans and leases | Other
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	94	40
90 Days Past Due and Still Accruing	0	0
Non- Accrual	0	1
Non-accrual with No ACL	0	0
Total commercial loans and leases | Other | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	0	0
Total commercial loans and leases | Other | Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	0	1
Total commercial loans and leases | Other | Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	94	39
Total consumer loans
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	8,503	7,989
90 Days Past Due and Still Accruing	6	16
Non- Accrual	24	38
Non-accrual with No ACL	0	0
Total consumer loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	43	49
Total consumer loans | Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	73	103
Total consumer loans | Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	8,430	7,886
Total consumer loans | Direct installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	2,376	2,020
90 Days Past Due and Still Accruing	0	2
Non- Accrual	7	11
Non-accrual with No ACL	0	0
Total consumer loans | Direct installment | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	5	7
Total consumer loans | Direct installment | Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	12	20
Total consumer loans | Direct installment | Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	2,364	2,000
Total consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	3,654	3,433
90 Days Past Due and Still Accruing	4	11
Non- Accrual	10	18
Non-accrual with No ACL	0	0
Total consumer loans | Residential mortgages | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	20	23
Total consumer loans | Residential mortgages | Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	34	52
Total consumer loans | Residential mortgages | Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	3,620	3,381
Total consumer loans | Indirect installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	1,227	1,218
90 Days Past Due and Still Accruing	1	1
Non- Accrual	2	2
Non-accrual with No ACL	0	0
Total consumer loans | Indirect installment | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	12	10
Total consumer loans | Indirect installment | Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	15	13
Total consumer loans | Indirect installment | Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	1,212	1,205
Total consumer loans | Consumer lines of credit
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	1,246	1,318
90 Days Past Due and Still Accruing	1	2
Non- Accrual	5	7
Non-accrual with No ACL	0	0
Total consumer loans | Consumer lines of credit | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	6	9
Total consumer loans | Consumer lines of credit | Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	12	18
Total consumer loans | Consumer lines of credit | Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	$ 1,234	$ 1,300