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, 2024	Dec. 31, 2023
Intangible Assets [Line Items]
Gross Carrying Amount	$ 427	$ 427
Accumulated Amortization	(252)	(241)
Net Carrying Value	175	186
Core deposit intangibles
Intangible Assets [Line Items]
Gross Carrying Amount	368	368
Accumulated Amortization	(218)	(208)
Net Carrying Value	150	160
Client relationships
Intangible Assets [Line Items]
Gross Carrying Amount	32	32
Accumulated Amortization	(16)	(16)
Net Carrying Value	16	16
Other
Intangible Assets [Line Items]
Gross Carrying Amount	27	27
Accumulated Amortization	(18)	(17)
Net Carrying Value	$ 9	$ 10