Loans and asset quality - Loan Distribution and Industry Concentrations (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 55,397	$ 54,953
Unearned income on lease financings	292	313
Other residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	450	494
Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		2,700
Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	12,900	13,400
Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	42,893	42,548
Domestic | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,192	1,442
Domestic | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,217	5,575
Domestic | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,804	4,852
Domestic | Lease financings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	439	537
Domestic | Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	15,753	16,050
Domestic | Other residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	450	494
Domestic | Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,073	524
Domestic | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,489	1,167
Domestic | Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	11,476	11,907
Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	12,504	12,405
Foreign | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	253	347
Foreign | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	11	7
Foreign | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,949	7,626
Foreign | Lease financings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	589	576
Foreign | Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	122	140
Foreign | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,147	2,230
Foreign | Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 1,433	$ 1,479