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Goodwill and Other Intangible Assets - Changes In The Carrying Amount Of Goodwill (Details) € in Millions, $ in Millions	3 Months Ended			9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2021 EUR (€)	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Goodwill [Roll Forward]
Beginning balance		$ 7,683		$ 7,683	$ 7,556
Foreign currency translation				(82)	127
Acquisitions				66
Divestitures				(17)
Ending balance	$ 7,650			7,650	7,683
Investment Servicing
Goodwill [Roll Forward]
Beginning balance		7,413		7,413	7,289
Foreign currency translation				(80)	124
Acquisitions				66
Divestitures				(17)
Ending balance	7,382			7,382	7,413
Investment Servicing \| Fideuram Bank Luxembour
Goodwill [Roll Forward]
Payment for acquisition		258	€ 220
Investment Servicing \| Mercatus, Inc
Goodwill [Roll Forward]
Payment for acquisition	88
Investment Management
Goodwill [Roll Forward]
Beginning balance		$ 270		270	267
Foreign currency translation				(2)	3
Acquisitions				0
Divestitures				0
Ending balance	$ 268			$ 268	$ 270