Derivative instruments - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 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	$ 168,000,000
Gain or (loss) recognized in income on derivatives	$ (15,000,000)	$ 22,000,000	$ (6,000,000)
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	$ 30,000,000	63,000,000
Foreign exchange contracts | Net investment hedging
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Hedged financial instruments, notional amount of derivative	7,200,000,000
Foreign exchange contracts | Forecasted Foreign Currency | Cash flow hedges
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Hedged financial instruments, notional amount of derivative	$ 291,000,000
Original maturities, maximum, of hedged instruments	12 months
Pre-tax gain (loss) recognized in OCI related to cash flow hedges	$ (10,000,000)
Securities available-for-sale | Interest rate swap
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Hedged financial instruments	16,500,000,000
Hedged financial instruments, notional amount of derivative	16,500,000,000
Long-term debt
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Hedged financial instruments	13,900,000,000
Long-term debt | Interest rate swap
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Hedged financial instruments, notional amount of derivative	$ 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	$ (41,000,000)	$ 13,000,000	18,000,000
Securities available-for-sale | Foreign exchange contracts
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Gain from components excluded from assessment of fair value hedge effectiveness, net	$ 1,000,000		$ 1,000,000