Loans and asset quality - Allowance for Credit Losses Activity (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 252	$ 261	$ 281
Charge-offs	(14)	(1)	(1)
Recoveries	3	3	5
Net (charge-offs) recoveries	(11)	2	4
Provision	(25)	(11)	(24)
Ending balance	216	252	261
Allowance for:
Loan losses	122	146	159
Lending-related commitments	94	106	102
Individually evaluated for impairment:
Loan balance	15	4	6
Allowance for loan losses	0	0	1
Collectively evaluated for impairment:
Loan balance	54,938	56,560	61,534
Allowance for loan losses	122	146	158
Loans	54,953	56,564
Commercial
Collectively evaluated for impairment:
Loans	1,800
Financial institutions
Collectively evaluated for impairment:
Loans	12,500
Wealth management loans and mortgages
Collectively evaluated for impairment:
Loans	16,190	15,965
Other residential mortgages
Collectively evaluated for impairment:
Loans	494	594
Overdrafts
Collectively evaluated for impairment:
Loans	2,700	5,500
Margin loans
Collectively evaluated for impairment:
Loans	13,400	13,500
Domestic
Collectively evaluated for impairment:
Loans	42,548	45,044
Domestic \| Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	81	77	82
Charge-offs	(12)	0	0
Recoveries	0	0	0
Net (charge-offs) recoveries	(12)	0	0
Provision	(9)	4	(5)
Ending balance	60	81	77
Allowance for:
Loan losses	11	24	24
Lending-related commitments	49	57	53
Individually evaluated for impairment:
Loan balance	0	0	0
Allowance for loan losses	0	0	0
Collectively evaluated for impairment:
Loan balance	1,442	1,949	2,744
Allowance for loan losses	11	24	24
Loans	1,442	1,949
Domestic \| Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	75	76	73
Charge-offs	0	0	0
Recoveries	0	0	0
Net (charge-offs) recoveries	0	0	0
Provision	1	(1)	3
Ending balance	76	75	76
Allowance for:
Loan losses	57	56	58
Lending-related commitments	19	19	18
Individually evaluated for impairment:
Loan balance	0	0	0
Allowance for loan losses	0	0	0
Collectively evaluated for impairment:
Loan balance	5,575	4,787	4,900
Allowance for loan losses	57	56	58
Loans	5,575	4,787
Domestic \| Financial institutions
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	22	23	26
Charge-offs	0	0	0
Recoveries	0	0	0
Net (charge-offs) recoveries	0	0	0
Provision	(2)	(1)	(3)
Ending balance	20	22	23
Allowance for:
Loan losses	5	7	7
Lending-related commitments	15	15	16
Individually evaluated for impairment:
Loan balance	0	0	1
Allowance for loan losses	0	0	0
Collectively evaluated for impairment:
Loan balance	4,852	5,091	5,567
Allowance for loan losses	5	7	7
Loans	4,852	5,091
Domestic \| Lease financings
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	5	8	13
Charge-offs	0	0	0
Recoveries	0	0	0
Net (charge-offs) recoveries	0	0	0
Provision	(2)	(3)	(5)
Ending balance	3	5	8
Allowance for:
Loan losses	3	5	8
Lending-related commitments	0	0	0
Individually evaluated for impairment:
Loan balance	0	0	0
Allowance for loan losses	0	0	0
Collectively evaluated for impairment:
Loan balance	537	706	772
Allowance for loan losses	3	5	8
Loans	537	706
Domestic \| Wealth management loans and mortgages
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	21	22	23
Charge-offs	(1)	0	0
Recoveries	0	0	0
Net (charge-offs) recoveries	(1)	0	0
Provision	0	(1)	(1)
Ending balance	20	21	22
Allowance for:
Loan losses	18	18	18
Lending-related commitments	2	3	4
Individually evaluated for impairment:
Loan balance	15	4	5
Allowance for loan losses	0	0	1
Collectively evaluated for impairment:
Loan balance	16,035	15,839	16,415
Allowance for loan losses	18	18	17
Loans	16,050	15,843
Domestic \| Other residential mortgages
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	16	20	28
Charge-offs	(1)	(1)	(1)
Recoveries	3	2	5
Net (charge-offs) recoveries	2	1	4
Provision	(5)	(5)	(12)
Ending balance	13	16	20
Allowance for:
Loan losses	13	16	20
Lending-related commitments	0	0	0
Individually evaluated for impairment:
Loan balance	0	0	0
Allowance for loan losses	0	0	0
Collectively evaluated for impairment:
Loan balance	494	594	708
Allowance for loan losses	13	16	20
Loans	494	594
Domestic \| All other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	0	0	0
Charge-offs	0	0	0
Recoveries	0	0	0
Net (charge-offs) recoveries	0	0	0
Provision	0	0	0
Ending balance	0	0	0
Allowance for:
Loan losses	0	0	0
Lending-related commitments	0	0	0
Individually evaluated for impairment:
Loan balance	0	0	0
Allowance for loan losses	0	0	0
Collectively evaluated for impairment:
Loan balance	13,598	16,074	17,783
Allowance for loan losses	0	0	0
Domestic \| Overdrafts
Collectively evaluated for impairment:
Loans	524	1,550	963
Domestic \| Margin loans
Collectively evaluated for impairment:
Loans	11,907	13,343	15,689
Domestic \| Other
Collectively evaluated for impairment:
Loans	1,167	1,181	1,131
Foreign
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	32	35	36
Charge-offs	0	0	0
Recoveries	0	1	0
Net (charge-offs) recoveries	0	1	0
Provision	(8)	(4)	(1)
Ending balance	24	32	35
Allowance for:
Loan losses	15	20	24
Lending-related commitments	9	12	11
Individually evaluated for impairment:
Loan balance	0	0	0
Allowance for loan losses	0	0	0
Collectively evaluated for impairment:
Loan balance	12,405	11,520	12,645
Allowance for loan losses	15	20	$ 24
Loans	12,405	11,520
Foreign \| Commercial
Collectively evaluated for impairment:
Loans	347	183
Foreign \| Commercial real estate
Collectively evaluated for impairment:
Loans	7	0
Foreign \| Financial institutions
Collectively evaluated for impairment:
Loans	7,626	6,492
Foreign \| Lease financings
Collectively evaluated for impairment:
Loans	576	551
Foreign \| Wealth management loans and mortgages
Collectively evaluated for impairment:
Loans	140	122
Foreign \| Margin loans
Collectively evaluated for impairment:
Loans	1,479	141
Foreign \| Other
Collectively evaluated for impairment:
Loans	$ 2,230	$ 4,031

Financing Receivable, Allowance for Credit Losses, Unfunded Commitments

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Loans and Allowance for Loan Losses Collectively Evalueated for Impairment [Abstract]

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Amount, after recovery, of writeoff of financing receivable, charged against allowance for credit loss.

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Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

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