Loans and asset quality - Credit Risk Indicators Narrative (Details) - USD ($)	9 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of exposure to investment grade securities	95.00%
Percentage of financial institution exposure secured	75.00%
Percent of financial institution exposure expiring within one year	89.00%
Loans	$ 55,491,000,000	$ 54,953,000,000
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)	22.00%
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)	43.00%
Other residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 423,000,000	494,000,000
Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		2,700,000,000
Overdraft repayment period	2 days
Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 13,500,000,000	13,400,000,000
Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	43,186,000,000	42,548,000,000
Domestic \| Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	15,805,000,000	16,050,000,000
Domestic \| Other residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	423,000,000	494,000,000
Purchased mortgages	76,000,000
Domestic \| Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	899,000,000	524,000,000
Domestic \| Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 11,220,000,000	11,907,000,000
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)	19.00%
Overdrafts \| Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 3,963,000,000
Operating segments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	55,491,000,000	$ 54,953,000,000
Federal funds sold and securities purchased under resale agreements, allowance for credit losses	$ 0

Federal Funds Sold and Securities Purchased under Agreements to Resell, Allowance for Credit Losses

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Loan To Value Ratio

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Percentage Collateral To Loans

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Percentage of Exposure to Investment Grade Securities

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Percentage of Financial Institution Exposure Secured

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Percent of Financial Institution Exposure Expiring Within One Year

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Purchased residential mortgages.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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