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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				12 Months Ended
	Mar. 31, 2022 USD ($)	Sep. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2021 EUR (€)	Dec. 31, 2021 USD ($)
Finite-lived Intangible Assets [Roll Forward]
Beginning balance	$ 1,816		$ 1,827		$ 1,827
Acquisitions	0				264
Amortization	(61)		(58)		(245)
Foreign currency translation	(11)				(30)
Ending balance	1,744				1,816
Investment Servicing
Finite-lived Intangible Assets [Roll Forward]
Beginning balance	1,746		1,733		1,733
Acquisitions	0				264
Amortization	(55)				(221)
Foreign currency translation	(11)				(30)
Ending balance	1,680				1,746
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	70		$ 94		94
Acquisitions	0				0
Amortization	(6)				(24)
Foreign currency translation	0				0
Ending balance	$ 64				$ 70