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Goodwill and Other Intangible Assets - Changes In The Carrying Amount Of Other Intangible Assets (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, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Finite-lived Intangible Assets [Roll Forward]
Beginning balance		$ 1,827			$ 1,827	$ 2,030	$ 2,030
Amortization	$ (62)			$ (59)	(183)	(175)	(234)
Foreign currency translation					(20)		31
Acquisitions					263
Ending balance	1,887				1,887		1,827
Investment Servicing
Finite-lived Intangible Assets [Roll Forward]
Beginning balance		1,733			1,733	1,908	1,908
Amortization					(165)		(206)
Foreign currency translation					(20)		31
Acquisitions					263
Ending balance	1,811				1,811		1,733
Investment Servicing \| Fideuram Bank Luxembour
Finite-lived Intangible Assets [Roll Forward]
Payment for acquisition		258	€ 220
Investment Servicing \| Mercatus, Inc
Finite-lived Intangible Assets [Roll Forward]
Payment for acquisition	88
Investment Management
Finite-lived Intangible Assets [Roll Forward]
Beginning balance		$ 94			94	$ 122	122
Amortization					(18)		(28)
Foreign currency translation					0		0
Acquisitions					0
Ending balance	$ 76				$ 76		$ 94