Goodwill and Other Intangible Assets - Schedule of Intangible Assets and Accumulated Amortization Included in the Consolidated Statements of Condition (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Intangible Assets [Line Items]
Gross Carrying Amount	$ 397	$ 397
Accumulated Amortization	(300)	(292)
Net Carrying Value	97	105
Core deposit intangibles
Intangible Assets [Line Items]
Gross Carrying Amount	354	354
Accumulated Amortization	(271)	(264)
Net Carrying Value	83	90
Client relationships
Intangible Assets [Line Items]
Gross Carrying Amount	32	32
Accumulated Amortization	(21)	(20)
Net Carrying Value	11	12
Other
Intangible Assets [Line Items]
Gross Carrying Amount	11	11
Accumulated Amortization	(8)	(8)
Net Carrying Value	$ 3	$ 3