Accounting changes and new accounting guidance - Narrative (Details) - USD ($)	9 Months Ended				12 Months Ended
	Sep. 30, 2020		Sep. 30, 2019		Dec. 31, 2019		Dec. 31, 2018		Jun. 30, 2020		Mar. 31, 2020		Jan. 01, 2020	Jun. 30, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201602Member		us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201802Member
Adjustment for the cumulative effect of applying the ASU	$ 45,168,000,000	[1],[2]	$ 41,323,000,000	[3],[4]	$ 41,585,000,000	[1]	$ 40,739,000,000	[3]	$ 43,809,000,000	[2],[5]	$ 41,239,000,000	[5]		$ 41,699,000,000	[4]
Minimum loan amount required to measure impairment allowance	1,000,000
Retained earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment for the cumulative effect of applying the ASU	$ 33,821,000,000		$ 30,789,000,000		31,894,000,000		28,652,000,000		$ 33,224,000,000		$ 32,601,000,000			$ 30,081,000,000
Commercial Loan
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Threshold period past due for nonaccrual status	90 days
First Lien Residential Mortgage
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Threshold period past due subject to impairment test	90 days
Second Lien Residential Mortgage
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Threshold period past due subject to further impairment testing	90 days
Cumulative Effect, Period Of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment for the cumulative effect of applying the ASU					40,000,000		0
Cumulative Effect, Period Of Adoption, Adjustment | Retained earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment for the cumulative effect of applying the ASU					$ 45,000,000		$ 90,000,000						$ 45,000,000

[1] Includes total The Bank of New York Mellon Corporation common shareholders’ equity of $37,941 million at Dec. 31, 2019 and $40,385 million at Sept. 30, 2020.

[2] Includes total The Bank of New York Mellon Corporation common shareholders’ equity of $39,165 million at June 30, 2020 and $40,385 million at Sept. 30, 2020.

[3] Includes total The Bank of New York Mellon Corporation common shareholders’ equity of $37,096 million at Dec. 31, 2018 and $37,578 million at Sept. 30, 2019.

[4] Includes total The Bank of New York Mellon Corporation common shareholders’ equity of $37,991 million at June 30, 2019 and $37,578 million at Sept. 30, 2019.

[5] Includes total The Bank of New York Mellon Corporation common shareholders’ equity of $37,603 million at March 31, 2020 and $39,165 million at June 30, 2020.