Goodwill and Other Intangible Assets - Gross Carrying Amount, Accumulated Amortization And Net Carrying Amount Of Other Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 3,806	$ 4,280
Accumulated Amortization	(1,843)	(2,250)
Net Carrying Amount	1,963	2,030	$ 2,369
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2,636	3,104
Accumulated Amortization	(1,294)	(1,718)
Net Carrying Amount	1,342	1,386
Technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	403	403
Accumulated Amortization	(96)	(87)
Net Carrying Amount	307	316
Core deposits
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	669	673
Accumulated Amortization	(388)	(381)
Net Carrying Amount	281	292
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	98	100
Accumulated Amortization	(65)	(64)
Net Carrying Amount	$ 33	$ 36