Loans and asset quality - Allowance for Credit Losses Activity (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2025	Jun. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 345	$ 370	$ 359	$ 366	$ 390
Charge-offs	(5)	(10)	(10)	(25)	(54)
Recoveries	1	5	0	7	0
Net (charge-offs) recoveries	(4)	(5)	(10)	(18)	(54)
Provision	(6)	(20)	22	(13)	35
Ending balance	335	345	371	335	371
Allowance for loan losses	272	275	296	272	296	$ 294
Allowance for lending-related commitments	63	70	75	63	75	$ 72
Individually evaluated for impairment:
Loan balance	323	199	286	323	286
Allowance for loan losses	42	52	64	42	64
Provision (benefit) for other credit losses	(1)	3	1	7	15
Fair value of collateral	350	169	291	350	291
Asset Pledged as Collateral
Individually evaluated for impairment:
Loan balance	323	199	286	323	286
Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	13	15	27	20	27
Charge-offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Net (charge-offs) recoveries	0	0	0	0	0
Provision	(6)	(2)	3	(13)	3
Ending balance	7	13	30	7	30
Allowance for loan losses	1	2	16	1	16
Allowance for lending-related commitments	6	11	14	6	14
Individually evaluated for impairment:
Loan balance	0	0	0	0	0
Allowance for loan losses	0	0	0	0	0
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	291	326	298	315	325
Charge-offs	(5)	(10)	(10)	(25)	(53)
Recoveries	0	5	0	5	0
Net (charge-offs) recoveries	(5)	(5)	(10)	(20)	(53)
Provision	4	(30)	20	(5)	36
Ending balance	290	291	308	290	308
Allowance for loan losses	247	245	258	247	258
Allowance for lending-related commitments	43	46	50	43	50
Individually evaluated for impairment:
Loan balance	315	198	273	315	273
Allowance for loan losses	42	52	64	42	64
Financial institutions
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	25	16	21	19	19
Charge-offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Net (charge-offs) recoveries	0	0	0	0	0
Provision	(3)	9	0	3	2
Ending balance	22	25	21	22	21
Allowance for loan losses	10	13	12	10	12
Allowance for lending-related commitments	12	12	9	12	9
Individually evaluated for impairment:
Loan balance	0	0	0	0	0
Allowance for loan losses	0	0	0	0	0
Lease financings
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance					1
Charge-offs					0
Recoveries					0
Net (charge-offs) recoveries					0
Provision					(1)
Ending balance			0		0
Wealth management loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1	1	1	1	1
Charge-offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Net (charge-offs) recoveries	0	0	0	0	0
Provision	0	0	0	0	0
Ending balance	1	1	1	1	1
Allowance for loan losses	1	1	1	1	1
Allowance for lending-related commitments	0	0	0	0	0
Individually evaluated for impairment:
Loan balance	0	0	0	0	0
Allowance for loan losses	0	0	0	0	0
Wealth management mortgages
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	6	6	6	6	9
Charge-offs	0	0	0	0	(1)
Recoveries	0	0	0	0	0
Net (charge-offs) recoveries	0	0	0	0	(1)
Provision	0	0	0	0	(2)
Ending balance	6	6	6	6	6
Allowance for loan losses	6	6	5	6	5
Allowance for lending-related commitments	0	0	1	0	1
Individually evaluated for impairment:
Loan balance	8	1	13	8	13
Allowance for loan losses	0	0	0	0	0
Other residential mortgages
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	2	2	3	2	4
Charge-offs	0	0	0	0	0
Recoveries	1	0	0	2	0
Net (charge-offs) recoveries	1	0	0	2	0
Provision	(1)	0	(1)	(2)	(2)
Ending balance	2	2	2	2	2
Allowance for loan losses	2	2	2	2	2
Allowance for lending-related commitments	0	0	0	0	0
Individually evaluated for impairment:
Loan balance	0	0	0	0	0
Allowance for loan losses	0	0	0	0	0
Capital call financing
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	7	4	3	3	4
Charge-offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Net (charge-offs) recoveries	0	0	0	0	0
Provision	0	3	0	4	(1)
Ending balance	7	7	3	7	3
Allowance for loan losses	5	6	2	5	2
Allowance for lending-related commitments	2	1	1	2	1
Individually evaluated for impairment:
Loan balance	0	0	0	0	0
Allowance for loan losses	$ 0	$ 0	$ 0	$ 0	$ 0

Financing Receivable, Allowance for Credit Loss and Off Balance Sheet Credit Loss, Liability

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Financing Receivable, Allowance for Credit Loss and Off Balance Sheet Credit Loss, Liability, Expense (Reversal)

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Financing Receivable, Allowance for Credit Loss and Off Balance Sheet Credit Loss, Liability, Recovery

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Financing Receivable, Allowance for Credit Loss and Off Balance Sheet Credit Loss, Liability, Writeoff

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Financing Receivable, Allowance for Credit Loss and Off Balance Sheet Credit Loss, Liability, Writeoff, after Recovery

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- Definition

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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-Name Accounting Standards Codification
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Amount of allowance for credit loss on financing receivable evaluated on individual basis. Excludes financing receivable evaluated on collective basis.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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Amount of financing receivable individually evaluated for credit loss. Excludes financing receivable collectively evaluated for credit loss.

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- Definition

Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

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Amount of expense related to credit loss from transactions other than loan and lease transactions.

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- Definition

Fair value of the securities pledged as collateral against securities loaned.

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