Allowance for Credit Losses - Summary of loans in Accrual and Nonaccrual Status (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 132,122	$ 129,492
30-89 Days Past Due	1,724	1,779
Accruing Loans Past Due 90 Days or More	339	491
Nonaccrual	2,166	2,439
Loans and leases, net of unearned discount	134,068	131,564
Gross charge-offs	570
Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	29,237	26,199
Gross charge-offs	40
Revolving Loans Converted to Term Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,619	1,664
Gross charge-offs	5
Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	763	596
Accruing Loans Past Due 90 Days or More	295	345
Nonaccrual	215	272
Loans and leases, net of unearned discount	22,353	22,705
Gross charge-offs	8
Residential [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due		1
Nonaccrual	1	6
Loans and leases, net of unearned discount	96	38
Residential Limited Documentation [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	31	22
Nonaccrual	55	78
Loans and leases, net of unearned discount	911	1,051
Gross charge-offs	2
Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	40	31
Nonaccrual	81	85
Loans and leases, net of unearned discount	4,649	5,007
Gross charge-offs	6
Home Equity Lines and Loans [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Nonaccrual	3	3
Loans and leases, net of unearned discount	3,025	3,267
Gross charge-offs	1
Home Equity Lines and Loans [Member] | Revolving Loans Converted to Term Loans [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	37	28
Nonaccrual	73	75
Loans and leases, net of unearned discount	1,501	1,590
Gross charge-offs	5
Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	9,935
30-89 Days Past Due	87	55
Nonaccrual	36	45
Loans and leases, net of unearned discount	10,058	9,074
Gross charge-offs	68
Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	60	44
Nonaccrual	14	40
Loans and leases, net of unearned discount	3,992	4,477
Gross charge-offs	23
Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,003
30-89 Days Past Due	30	23
Accruing Loans Past Due 90 Days or More	7	5
Nonaccrual	52	49
Loans and leases, net of unearned discount	2,092	2,034
Gross charge-offs	78
Other [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,392
30-89 Days Past Due	20	16
Accruing Loans Past Due 90 Days or More	7	5
Nonaccrual	48	45
Loans and leases, net of unearned discount	1,467	1,440
Gross charge-offs	20
Other [Member] | Revolving Loans Converted to Term Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3
30-89 Days Past Due	1	1
Nonaccrual
Loans and leases, net of unearned discount	4	9
Current [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	129,839	126,855
Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	21,080	21,492
Current [Member] | Residential [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	95	31
Current [Member] | Residential Limited Documentation [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	825	951
Current [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	4,528	4,891
Current [Member] | Home Equity Lines and Loans [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3,022	3,264
Current [Member] | Home Equity Lines and Loans [Member] | Revolving Loans Converted to Term Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,391	1,487
Current [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	9,935	8,974
Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3,918	4,393
Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,003	1,957
Current [Member] | Other [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		1,374
Current [Member] | Other [Member] | Revolving Loans Converted to Term Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		8
Term Loans 2023 [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	18,423
Gross charge-offs	34
Term Loans 2023 [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	18
Accruing Loans Past Due 90 Days or More	1
Nonaccrual	1
Loans and leases, net of unearned discount	1,746
Term Loans 2023 [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,653
30-89 Days Past Due	11
Nonaccrual	3
Loans and leases, net of unearned discount	2,667
Gross charge-offs	4
Term Loans 2023 [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	8
Nonaccrual	2
Loans and leases, net of unearned discount	1,073
Gross charge-offs	2
Term Loans 2023 [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	250
30-89 Days Past Due	3
Nonaccrual	2
Loans and leases, net of unearned discount	255
Gross charge-offs	18
Term Loans 2023 [Member] | Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,726
Term Loans 2023 [Member] | Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,063
Term Loans 2022 [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,683	24,854
Gross charge-offs	81
Term Loans 2022 [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	120	60
Accruing Loans Past Due 90 Days or More	30	12
Nonaccrual	17	6
Loans and leases, net of unearned discount	4,876	5,149
Term Loans 2022 [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount		1
Term Loans 2022 [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,338
30-89 Days Past Due	16	9
Nonaccrual	5	3
Loans and leases, net of unearned discount	2,359	2,854
Gross charge-offs	13
Term Loans 2022 [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	15	7
Nonaccrual	3	2
Loans and leases, net of unearned discount	1,114	1,500
Gross charge-offs	6
Term Loans 2022 [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	176
30-89 Days Past Due	3	4
Nonaccrual	1	3
Loans and leases, net of unearned discount	180	281
Gross charge-offs	17
Term Loans 2022 [Member] | Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	4,709	5,071
Term Loans 2022 [Member] | Current [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		1
Term Loans 2022 [Member] | Current [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		2,842
Term Loans 2022 [Member] | Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,096	1,491
Term Loans 2022 [Member] | Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		274
Term Loans 2021 [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	15,025	18,749
Gross charge-offs	47
Term Loans 2021 [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	88	51
Accruing Loans Past Due 90 Days or More	28	40
Nonaccrual	10	11
Loans and leases, net of unearned discount	3,858	4,104
Gross charge-offs	1
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]
Total loans	1,857
30-89 Days Past Due	19	10
Nonaccrual	8	7
Loans and leases, net of unearned discount	1,884	2,298
Gross charge-offs	14
Term Loans 2021 [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	17	13
Nonaccrual	3	11
Loans and leases, net of unearned discount	1,067	1,582
Gross charge-offs	7
Term Loans 2021 [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	118
30-89 Days Past Due	2	1
Nonaccrual	1	1
Loans and leases, net of unearned discount	121	175
Gross charge-offs	7
Term Loans 2021 [Member] | Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3,732	4,002
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		2,281
Term Loans 2021 [Member] | Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,047	1,558
Term Loans 2021 [Member] | Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		173
Term Loans 2020 [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	10,555	13,071
Gross charge-offs	31
Term Loans 2020 [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	52	40
Accruing Loans Past Due 90 Days or More	17	20
Nonaccrual	3	3
Loans and leases, net of unearned discount	2,615	2,780
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]
Total loans	1,286
30-89 Days Past Due	14	12
Nonaccrual	6	9
Loans and leases, net of unearned discount	1,306	1,609
Gross charge-offs	12
Term Loans 2020 [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	9	7
Nonaccrual	2	7
Loans and leases, net of unearned discount	438	717
Gross charge-offs	3
Term Loans 2020 [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	33
Loans and leases, net of unearned discount	33	58
Gross charge-offs	3
Term Loans 2020 [Member] | Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,543	2,717
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		1,588
Term Loans 2020 [Member] | Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	427	703
Term Loans 2020 [Member] | Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		58
Term Loans 2019 [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	10,062	12,738
Gross charge-offs	142
Term Loans 2019 [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	28	22
Accruing Loans Past Due 90 Days or More	14	14
Nonaccrual	4	10
Loans and leases, net of unearned discount	1,261	1,439
Gross charge-offs	3
Term Loans 2019 [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Nonaccrual		1
Loans and leases, net of unearned discount	13	16
Term Loans 2019 [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	781
30-89 Days Past Due	11	8
Nonaccrual	5	8
Loans and leases, net of unearned discount	797	980
Gross charge-offs	9
Term Loans 2019 [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	6	7
Nonaccrual	2	8
Loans and leases, net of unearned discount	206	394
Gross charge-offs	2
Term Loans 2019 [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	13
Loans and leases, net of unearned discount	13	39
Gross charge-offs	3
Term Loans 2019 [Member] | Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,215	1,393
Term Loans 2019 [Member] | Current [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	13	15
Term Loans 2019 [Member] | Current [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		964
Term Loans 2019 [Member] | Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	198	379
Term Loans 2019 [Member] | Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		39
Term Loans 2018 [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount		7,535
Term Loans 2018 [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due		23
Accruing Loans Past Due 90 Days or More		14
Nonaccrual		5
Loans and leases, net of unearned discount		796
Term Loans 2018 [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due		1
Loans and leases, net of unearned discount		24
Term Loans 2018 [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due		5
Nonaccrual		6
Loans and leases, net of unearned discount		498
Term Loans 2018 [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due		6
Nonaccrual		6
Loans and leases, net of unearned discount		179
Term Loans 2018 [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount		8
Term Loans 2018 [Member] | Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		754
Term Loans 2018 [Member] | Current [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		23
Term Loans 2018 [Member] | Current [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		487
Term Loans 2018 [Member] | Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		167
Term Loans 2018 [Member] | Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		8
Term Loans Prior Period [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	27,464	26,754
Gross charge-offs	190
Term Loans Prior Period [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	457	399
Accruing Loans Past Due 90 Days or More	205	245
Nonaccrual	179	231
Loans and leases, net of unearned discount	7,901	8,399
Gross charge-offs	4
Term Loans Prior Period [Member] | Residential Limited Documentation [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	31	22
Nonaccrual	55	78
Loans and leases, net of unearned discount	911	1,051
Gross charge-offs	2
Term Loans Prior Period [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	3	2
Nonaccrual	5	6
Loans and leases, net of unearned discount	106	105
Term Loans Prior Period [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,020
30-89 Days Past Due	16	11
Nonaccrual	9	12
Loans and leases, net of unearned discount	1,045	835
Gross charge-offs	16
Term Loans Prior Period [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
30-89 Days Past Due	5	4
Nonaccrual	2	6
Loans and leases, net of unearned discount	94	105
Gross charge-offs	3
Term Loans Prior Period [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	18
30-89 Days Past Due	1	1
Loans and leases, net of unearned discount	19	24
Gross charge-offs	10
Term Loans Prior Period [Member] | Current [Member] | Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	7,060	7,524
Term Loans Prior Period [Member] | Current [Member] | Residential Limited Documentation [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	825	951
Term Loans Prior Period [Member] | Current [Member] | Home Equity Lines and Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	98	97
Term Loans Prior Period [Member] | Current [Member] | Recreational Finance [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		812
Term Loans Prior Period [Member] | Current [Member] | Automobile [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 87	95
Term Loans Prior Period [Member] | Current [Member] | Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		$ 23