Derivative instruments - Narrative (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Counterparty default losses recorded	$ 0
Hedging derivatives, maturities, maximum				1 year
Non-derivative financial instruments designated as hedges of net investments in foreign subsidiaries were all long-term liabilities of BNY Mellon in various currencies				$ 179,000,000
Gain or (loss) recognized in income on derivatives	10,000,000	$ (1,000,000)	$ (5,000,000)	$ (6,000,000)	$ (15,000,000)
Value-at-risk methodology assumed holding period for instruments				1 day
Value-at-risk methodology confidence level percentage				99.00%
Additional collateral The Bank of New York Mellon would have to post for existing collateral arrangements, if The Bank of New York Mellon had fallen below investment grade	31,000,000			$ 31,000,000		$ 63,000,000
Foreign exchange contracts | Net investment hedging
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Hedged financial instruments, notional amount of derivative	7,900,000,000			7,900,000,000
Foreign exchange contracts | Forecasted Foreign Currency
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Amount of pre-tax gain (loss) to be reclassified in the next 12 months from AOCI to earnings				5,000,000
Foreign exchange contracts | Forecasted Foreign Currency | Cash flow hedges
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Hedged financial instruments, notional amount of derivative	319,000,000			$ 319,000,000
Original maturities, maximum, of hedged instruments				15 months
Pre-tax gain (loss) recognized in OCI related to cash flow hedges				$ 5,000,000
Securities available-for-sale | Interest rate swap
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Hedged financial instruments	14,500,000,000			14,500,000,000
Hedged financial instruments, notional amount of derivative	14,500,000,000			14,500,000,000
Securities available-for-sale | Foreign currency forward
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Hedged financial instruments	140,000,000			140,000,000
Hedged financial instruments, notional amount of derivative	140,000,000			140,000,000
Long-term debt | Interest rate swap
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Hedged financial instruments	13,900,000,000			13,900,000,000
Hedged financial instruments, notional amount of derivative	13,900,000,000			$ 13,900,000,000
Original maturities, minimum, of hedged instruments				5 years
Original maturities, maximum, of hedged instruments				30 years
Not Designated as Hedging Instrument, Economic Hedge | Staff expense | Equity Swap
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Gain or (loss) recognized in income on derivatives	$ 12,000,000	$ 28,000,000		$ (1,000,000)	$ 23,000,000