Goodwill and Other Intangible Assets - Summary Of Intangible Assets and Accumulated Amortization Included In The Consolidated Statements of Condition (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Intangible Assets [Line Items]
Gross Carrying Amount	$ 449	$ 449
Accumulated Amortization	(110)	(95)
Net Carrying Value	339	354
Core deposit intangibles
Intangible Assets [Line Items]
Gross Carrying Amount	371	371
Accumulated Amortization	(93)	(81)
Net Carrying Value	278	290
Customer relationships
Intangible Assets [Line Items]
Gross Carrying Amount	37	37
Accumulated Amortization	(9)	(8)
Net Carrying Value	28	29
Other
Intangible Assets [Line Items]
Gross Carrying Amount	41	41
Accumulated Amortization	(8)	(6)
Net Carrying Value	$ 33	$ 35