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Loans and asset quality - Credit Risk Indicators Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of exposure to investment grade securities	96.00%
Percentage of financial institution exposure secured	79.00%
Percent of financial institution exposure expiring within one year	90.00%
Loans	$ 62,368		$ 54,953
Reverse repos fully secured	1,200
Allowance for credit loss	$ 288	$ 147	216	$ 224	$ 248	$ 252
Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan to value ratio at origination (percent)	62.00%
Percentage of past due mortgages (less than)	1.00%
Wealth management loans and mortgages \| California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Geographic concentrations (percent)	23.00%
Wealth management loans and mortgages \| New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Geographic concentrations (percent)	17.00%
Wealth management loans and mortgages \| Massachusetts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Geographic concentrations (percent)	10.00%
Wealth management loans and mortgages \| Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Geographic concentrations (percent)	8.00%
Wealth management loans and mortgages \| Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Geographic concentrations (percent)	42.00%
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
Overdraft repayment period	2 days
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 \| 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
Purchased mortgages	87
Domestic \| Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,851		524
Domestic \| Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 11,733		$ 11,907
Domestic \| Margin loans \| Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Required daily collateral margin (in excess of)	100.00%
Equal to or greater than 60 days past due \| Domestic \| Other residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of past due mortgages (less than)	9.00%
Overdrafts \| Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 6,147