Goodwill and Other Intangible Assets - Gross Carrying Amount, Accumulated Amortization And Net Carrying Amount Of Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 3,847	$ 4,280
Accumulated Amortization	(1,977)	(2,250)
Net Carrying Amount	1,870	2,030	$ 2,369
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2,671	3,104
Accumulated Amortization	(1,389)	(1,718)
Net Carrying Amount	1,282	1,386
Technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	392	403
Accumulated Amortization	(102)	(87)
Net Carrying Amount	290	316
Core deposits
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	681	673
Accumulated Amortization	(412)	(381)
Net Carrying Amount	269	292
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	103	100
Accumulated Amortization	(74)	(64)
Net Carrying Amount	$ 29	$ 36