Loans and Leases and the Allowance for Credit Losses - Summary of loans in Accrual and Nonaccrual Status (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	$ 1,410	$ 1,724
Accruing Loans Past Due 90 Days or More	297	339
Nonaccrual	2,302	2,166
Loans and leases, net of unearned discount	134,973	134,068
Gross charge-offs	163
Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	29,937	29,237
Gross charge-offs	68
Revolving Loans Converted to Term Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,595	1,619
Gross charge-offs	1
Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	627	763
Accruing Loans Past Due 90 Days or More	245	295
Nonaccrual	202	215
Loans and leases, net of unearned discount	22,192	22,353
Gross charge-offs	1
Residential [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Nonaccrual	1	1
Loans and leases, net of unearned discount	94	96
Residential Limited Documentation [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	30	31
Nonaccrual	53	55
Loans and leases, net of unearned discount	884	911
Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	34	40
Nonaccrual	87	81
Loans and leases, net of unearned discount	4,558	4,649
Gross charge-offs	1
Home Equity Lines and Loans [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Nonaccrual	1	3
Loans and leases, net of unearned discount	2,973	3,025
Home Equity Lines and Loans [Member] | Revolving Loans Converted to Term Loans [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	31	37
Nonaccrual	81	73
Loans and leases, net of unearned discount	1,468	1,501
Gross charge-offs	1
Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	71	87
Nonaccrual	30	36
Loans and leases, net of unearned discount	10,654	10,058
Gross charge-offs	25
Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	43	60
Nonaccrual	13	14
Loans and leases, net of unearned discount	4,308	3,992
Gross charge-offs	8
Other [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	20	30
Accruing Loans Past Due 90 Days or More	8	7
Nonaccrual	54	52
Loans and leases, net of unearned discount	2,064	2,092
Gross charge-offs	25
Other [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	12	20
Accruing Loans Past Due 90 Days or More	8	7
Nonaccrual	51	48
Loans and leases, net of unearned discount	1,449	1,467
Gross charge-offs	16
Other [Member] | Revolving Loans Converted to Term Loans [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	1	1
Loans and leases, net of unearned discount	2	4
Current [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	130,964	129,839
Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	21,118	21,080
Current [Member] | Residential [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	93	95
Current [Member] | Residential Limited Documentation [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	801	825
Current [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	4,437	4,528
Current [Member] | Home Equity Lines and Loans [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,972	3,022
Current [Member] | Home Equity Lines and Loans [Member] | Revolving Loans Converted to Term Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,356	1,391
Current [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	10,553	9,935
Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	4,252	3,918
Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,982	2,003
Current [Member] | Other [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,378	1,392
Current [Member] | Other [Member] | Revolving Loans Converted to Term Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1	3
Term Loans 2024 [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	5,121
Gross charge-offs	1
Term Loans 2024 [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	478
Term Loans 2024 [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	1
Loans and leases, net of unearned discount	1,029
Term Loans 2024 [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	1
Loans and leases, net of unearned discount	685
Term Loans 2024 [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	1
Nonaccrual	1
Loans and leases, net of unearned discount	71
Gross charge-offs	1
Term Loans 2024 [Member] | Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	478
Term Loans 2024 [Member] | Current [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,028
Term Loans 2024 [Member] | Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	684
Term Loans 2024 [Member] | Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	69
Term Loans 2023 [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	17,431	18,423
Gross charge-offs	15
Term Loans 2023 [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	6	18
Accruing Loans Past Due 90 Days or More	2	1
Nonaccrual	1	1
Loans and leases, net of unearned discount	1,508	1,746
Term Loans 2023 [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	11	11
Nonaccrual	4	3
Loans and leases, net of unearned discount	2,546	2,667
Gross charge-offs	3
Term Loans 2023 [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	7	8
Nonaccrual	2	2
Loans and leases, net of unearned discount	1,035	1,073
Gross charge-offs	2
Term Loans 2023 [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	1	3
Nonaccrual	1	2
Loans and leases, net of unearned discount	221	255
Gross charge-offs	3
Term Loans 2023 [Member] | Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,499	1,726
Term Loans 2023 [Member] | Current [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,531	2,653
Term Loans 2023 [Member] | Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,026	1,063
Term Loans 2023 [Member] | Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	219	250
Term Loans 2022 [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	20,835	21,683
Gross charge-offs	21
Term Loans 2022 [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	107	120
Accruing Loans Past Due 90 Days or More	21	30
Nonaccrual	15	17
Loans and leases, net of unearned discount	4,810	4,876
Term Loans 2022 [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	12	16
Nonaccrual	6	5
Loans and leases, net of unearned discount	2,270	2,359
Gross charge-offs	5
Term Loans 2022 [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	11	15
Nonaccrual	2	3
Loans and leases, net of unearned discount	1,017	1,114
Gross charge-offs	2
Term Loans 2022 [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	3	3
Nonaccrual	1	1
Loans and leases, net of unearned discount	159	180
Gross charge-offs	3
Term Loans 2022 [Member] | Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	4,667	4,709
Term Loans 2022 [Member] | Current [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,252	2,338
Term Loans 2022 [Member] | Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,004	1,096
Term Loans 2022 [Member] | Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	155	176
Term Loans 2021 [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	14,385	15,025
Gross charge-offs	13
Term Loans 2021 [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	62	88
Accruing Loans Past Due 90 Days or More	19	28
Nonaccrual	10	10
Loans and leases, net of unearned discount	3,808	3,858
Term Loans 2021 [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	2	2
Term Loans 2021 [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	14	19
Nonaccrual	6	8
Loans and leases, net of unearned discount	1,810	1,884
Gross charge-offs	6
Term Loans 2021 [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	11	17
Nonaccrual	3	3
Loans and leases, net of unearned discount	956	1,067
Gross charge-offs	2
Term Loans 2021 [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	1	2
Nonaccrual		1
Loans and leases, net of unearned discount	106	121
Gross charge-offs	1
Term Loans 2021 [Member] | Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3,717	3,732
Term Loans 2021 [Member] | Current [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2	2
Term Loans 2021 [Member] | Current [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,790	1,857
Term Loans 2021 [Member] | Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	942	1,047
Term Loans 2021 [Member] | Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	105	118
Term Loans 2020 [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	10,088	10,555
Gross charge-offs	9
Term Loans 2020 [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	30	52
Accruing Loans Past Due 90 Days or More	15	17
Nonaccrual	2	3
Loans and leases, net of unearned discount	2,580	2,615
Term Loans 2020 [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	2	2
Term Loans 2020 [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	13	14
Nonaccrual	4	6
Loans and leases, net of unearned discount	1,250	1,306
Gross charge-offs	4
Term Loans 2020 [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	6	9
Nonaccrual	2	2
Loans and leases, net of unearned discount	379	438
Gross charge-offs	1
Term Loans 2020 [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	28	33
Gross charge-offs	1
Term Loans 2020 [Member] | Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,533	2,543
Term Loans 2020 [Member] | Current [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2	2
Term Loans 2020 [Member] | Current [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,233	1,286
Term Loans 2020 [Member] | Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	371	427
Term Loans 2020 [Member] | Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	28	33
Term Loans 2019 [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount		10,062
Term Loans 2019 [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due		28
Accruing Loans Past Due 90 Days or More		14
Nonaccrual		4
Loans and leases, net of unearned discount		1,261
Term Loans 2019 [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount		13
Term Loans 2019 [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due		11
Nonaccrual		5
Loans and leases, net of unearned discount		797
Term Loans 2019 [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due		6
Nonaccrual		2
Loans and leases, net of unearned discount		206
Term Loans 2019 [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount		13
Term Loans 2019 [Member] | Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		1,215
Term Loans 2019 [Member] | Current [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		13
Term Loans 2019 [Member] | Current [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		781
Term Loans 2019 [Member] | Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		198
Term Loans 2019 [Member] | Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		13
Term Loans Prior Period [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	35,581	27,464
Gross charge-offs	35
Term Loans Prior Period [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	422	457
Accruing Loans Past Due 90 Days or More	188	205
Nonaccrual	173	179
Loans and leases, net of unearned discount	8,914	7,901
Gross charge-offs	1
Term Loans Prior Period [Member] | Residential Limited Documentation [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	30	31
Nonaccrual	53	55
Loans and leases, net of unearned discount	884	911
Term Loans Prior Period [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	3	3
Nonaccrual	5	5
Loans and leases, net of unearned discount	113	106
Term Loans Prior Period [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	20	16
Nonaccrual	10	9
Loans and leases, net of unearned discount	1,749	1,045
Gross charge-offs	7
Term Loans Prior Period [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	7	5
Nonaccrual	4	2
Loans and leases, net of unearned discount	236	94
Gross charge-offs	1
Term Loans Prior Period [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	1	1
Loans and leases, net of unearned discount	28	19
Term Loans Prior Period [Member] | Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8,131	7,060
Term Loans Prior Period [Member] | Current [Member] | Residential Limited Documentation [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	801	825
Term Loans Prior Period [Member] | Current [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	105	98
Term Loans Prior Period [Member] | Current [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,719	1,020
Term Loans Prior Period [Member] | Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	225	87
Term Loans Prior Period [Member] | Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 27	$ 18