Debt - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2026 USD ($) subsidiaryBusinessTrust class	Dec. 31, 2025 USD ($)
Debt Instrument [Line Items]
Number of classes of financial instruments | class	2
Number of business subsidiary trusts | subsidiaryBusinessTrust	2
Interest Rate Swap
Debt Instrument [Line Items]
Amount of hedged item	$ 20
ACST II | Junior Subordinated Debt, Preferred Securities
Debt Instrument [Line Items]
Basis spread on variable rate (in percent)	3.15%
ACST III
Debt Instrument [Line Items]
Basis spread on variable rate (in percent)	2.00%
Federal Reserve Bank Advances
Debt Instrument [Line Items]
Collateral, at carrying cost	$ 951	$ 939
Collateral, at fair value	718	707
Federal Home Loan Bank of New York
Debt Instrument [Line Items]
Collateral, at carrying cost	1,100	1,100
Collateral, at fair value	$ 943	$ 948