Loans and allowance for loan losses - Loan and Leases Considered Nonaccrual and Interest Income Recognized on Loans (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Mar. 31, 2025	Jan. 01, 2025	Dec. 31, 2024	Mar. 31, 2024	Jan. 01, 2024
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	$ 1,152	$ 1,056	$ 1,152	$ 1,056
Amortized Cost without Allowance	421	968	421	968
Total	1,573	2,024	1,573	2,024	$ 1,540	$ 1,690	$ 1,690	$ 2,302	$ 2,166
Amortized Cost	1,573	2,024	1,573	2,024	1,540	1,690	1,690	2,302	2,166
Interest Income Recognized	22	34	40	47
Commercial and industrial
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	663	494	663	494
Amortized Cost without Allowance	124	311	124	311
Total	787	805	787	805	662	696	696	864	670
Amortized Cost	787	805	787	805	662	696	696	864	670
Interest Income Recognized	6	7	12	9
Commercial Real Estate \| Commercial
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	289	315	289	315
Amortized Cost without Allowance	87	392	87	392
Total	376	707	376	707	394	468	468	855	869
Amortized Cost	376	707	376	707	394	468	468	855	869
Interest Income Recognized	10	20	17	26
Commercial Real Estate \| Residential builder and developer
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	1	2	1	2
Amortized Cost without Allowance	0	0	0	0
Total	1	2	1	2	1	2	2	3	3
Amortized Cost	1	2	1	2	1	2	2	3	3
Interest Income Recognized	0	0	0	0
Commercial Real Estate \| Other commercial construction
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	23	13	23	13
Amortized Cost without Allowance	0	64	0	64
Total	23	77	23	77	28	66	66	141	171
Amortized Cost	23	77	23	77	28	66	66	141	171
Interest Income Recognized	0	3	0	3
Residential Real Estate \| Residential
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	115	115	115	115
Amortized Cost without Allowance	150	145	150	145
Total	265	260	265	260	284	279	279	255	270
Amortized Cost	265	260	265	260	284	279	279	255	270
Interest Income Recognized	4	3	7	7
Consumer \| Home equity lines and loans
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	34	37	34	37
Amortized Cost without Allowance	41	42	41	42
Total	75	79	75	79	78	81	81	87	81
Amortized Cost	75	79	75	79	78	81	81	87	81
Interest Income Recognized	2	1	4	2
Consumer \| Recreational finance
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	15	15	15	15
Amortized Cost without Allowance	10	10	10	10
Total	25	25	25	25	26	31	31	30	36
Amortized Cost	25	25	25	25	26	31	31	30	36
Interest Income Recognized	0	0	0	0
Consumer \| Automobile
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	7	7	7	7
Amortized Cost without Allowance	2	4	2	4
Total	9	11	9	11	11	12	12	13	14
Amortized Cost	9	11	9	11	11	12	12	13	14
Interest Income Recognized	0	0	0	0
Consumer \| Other
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	5	58	5	58
Amortized Cost without Allowance	7	0	7	0
Total	12	58	12	58	56	55	55	54	52
Amortized Cost	12	58	12	58	$ 56	$ 55	$ 55	$ 54	$ 52
Interest Income Recognized	$ 0	$ 0	$ 0	$ 0

Financing Receivable, Excluding Accrued Interest, Nonaccrual, With Allowance

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- Definition

Impaired financing receivable nonaccrual interest income.

+ References

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- Definition

Amortized cost excluding accrued interest, of financing receivable on nonaccrual status. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-16

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- Definition

Amortized cost excluding accrued interest, of financing receivable on nonaccrual status with no allowance for credit loss. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-16

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