Goodwill and Other Intangible Assets - Summary of Intangible Assets and Accumulated Amortization Included in the Consolidated Statements of Condition (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Intangible Assets [Line Items]
Gross Carrying Amount	$ 427	$ 430
Accumulated Amortization	(229)	(196)
Net Carrying Value	198	234
Core deposit intangibles
Intangible Assets [Line Items]
Gross Carrying Amount	368	371
Accumulated Amortization	(199)	(171)
Net Carrying Value	169	200
Client relationships
Intangible Assets [Line Items]
Gross Carrying Amount	32	32
Accumulated Amortization	(15)	(13)
Net Carrying Value	17	19
Other
Intangible Assets [Line Items]
Gross Carrying Amount	27	27
Accumulated Amortization	(15)	(12)
Net Carrying Value	$ 12	$ 15