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, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Mar. 31, 2026	Jan. 01, 2026	Dec. 31, 2025	Mar. 31, 2025	Jan. 01, 2025
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	$ 890	$ 1,152	$ 890	$ 1,152
Amortized Cost without Allowance	318	421	318	421
Total	1,208	1,573	1,208	1,573	$ 1,240	$ 1,252	$ 1,252	$ 1,540	$ 1,690
Amortized Cost	1,208	1,573	1,208	1,573	1,240	1,252	1,252	1,540	1,690
Interest Income Recognized	22	22	34	40
Commercial and industrial
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	520	663	520	663
Amortized Cost without Allowance	50	124	50	124
Total	570	787	570	787	535	527	527	662	696
Amortized Cost	570	787	570	787	535	527	527	662	696
Interest Income Recognized	8	6	15	12
Commercial real estate \| Commercial
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	162	289	162	289
Amortized Cost without Allowance	54	87	54	87
Total	216	376	216	376	294	320	320	394	468
Amortized Cost	216	376	216	376	294	320	320	394	468
Interest Income Recognized	8	10	9	17
Commercial real estate \| Residential builder and developer
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	0	1	0	1
Amortized Cost without Allowance	0	0	0	0
Total	0	1	0	1	0	0	0	1	2
Amortized Cost	0	1	0	1	0	0	0	1	2
Interest Income Recognized	0	0	0	0
Commercial real estate \| Other commercial construction
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	29	23	29	23
Amortized Cost without Allowance	7	0	7	0
Total	36	23	36	23	10	13	13	28	66
Amortized Cost	36	23	36	23	10	13	13	28	66
Interest Income Recognized	0	0	0	0
Residential real estate \| Residential
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	111	115	111	115
Amortized Cost without Allowance	151	150	151	150
Total	262	265	262	265	272	264	264	284	279
Amortized Cost	262	265	262	265	272	264	264	284	279
Interest Income Recognized	4	4	6	7
Consumer \| Home equity lines and loans (e)
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	37	34	37	34
Amortized Cost without Allowance	40	41	40	41
Total	77	75	77	75	84	82	82	78	81
Amortized Cost	77	75	77	75	84	82	82	78	81
Interest Income Recognized	1	2	3	4
Consumer \| Recreational finance
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	19	15	19	15
Amortized Cost without Allowance	14	10	14	10
Total	33	25	33	25	32	30	30	26	31
Amortized Cost	33	25	33	25	32	30	30	26	31
Interest Income Recognized	1	0	1	0
Consumer \| Automobile
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	8	7	8	7
Amortized Cost without Allowance	2	2	2	2
Total	10	9	10	9	9	11	11	11	12
Amortized Cost	10	9	10	9	9	11	11	11	12
Interest Income Recognized	0	0	0	0
Consumer \| Other
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	4	5	4	5
Amortized Cost without Allowance	0	7	0	7
Total	4	12	4	12	4	5	5	56	55
Amortized Cost	4	12	4	12	$ 4	$ 5	$ 5	$ 56	$ 55
Interest Income Recognized	$ 0	$ 0	$ 0	$ 0

Financing Receivable, Excluding Accrued Interest, Nonaccrual, With Allowance

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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

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477657/942-210-S45-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478478/942-210-S50-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7)(e)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

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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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