Intangible Assets - Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 721	$ 726
Accumulated Amortization	(314)	(238)
Net Carrying Value	407	488
Core deposit intangible
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	700	700
Accumulated Amortization	(307)	(229)
Net Carrying Value	393	471
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	21	26
Accumulated Amortization	(7)	(9)
Net Carrying Value	$ 14	$ 17