Loans and asset quality - Loan Distribution and Industry Concentrations (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 62,368	$ 54,953
Unearned income on lease financings	301	313
Other residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	472	494
Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		2,700
Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	13,100	13,400
Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	47,494	42,548
Domestic | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,010	1,442
Domestic | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,429	5,575
Domestic | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,231	4,852
Domestic | Lease financings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	472	537
Domestic | Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	16,128	16,050
Domestic | Other residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	472	494
Domestic | Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,851	524
Domestic | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,168	1,167
Domestic | Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	11,733	11,907
Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	14,874	12,405
Foreign | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	425	347
Foreign | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	22	7
Foreign | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	7,985	7,626
Foreign | Lease financings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	582	576
Foreign | Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	131	140
Foreign | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,347	2,230
Foreign | Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 1,382	$ 1,479