Goodwill and Other Intangible Assets - Gross Carrying Amount, Accumulated Amortization And Net Carrying Amount Of Other Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 4,016	$ 3,894
Accumulated Amortization	(2,009)	(2,067)
Net Carrying Amount	2,007	1,827	$ 2,030
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2,827	2,704
Accumulated Amortization	(1,387)	(1,450)
Net Carrying Amount	1,440	1,254
Technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	386	393
Accumulated Amortization	(115)	(113)
Net Carrying Amount	271	280
Core deposits
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	699	690
Accumulated Amortization	(429)	(425)
Net Carrying Amount	270	265
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	104	107
Accumulated Amortization	(78)	(79)
Net Carrying Amount	$ 26	$ 28