Goodwill and Other Intangible Assets - Gross Carrying Amount, Accumulated Amortization And Net Carrying Amount Of Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 4,244	$ 4,430
Accumulated Amortization	(2,167)	(2,061)
Net Carrying Amount	2,077	2,369	$ 1,613
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	3,077	3,262
Accumulated Amortization	(1,659)	(1,605)
Net Carrying Amount	1,418	1,657
Technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	402	389
Accumulated Amortization	(77)	(49)
Net Carrying Amount	325	340
Core deposits
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	667	676
Accumulated Amortization	(370)	(350)
Net Carrying Amount	297	326
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	98	103
Accumulated Amortization	(61)	(57)
Net Carrying Amount	$ 37	$ 46