Debt - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2025 USD ($) subsidiaryBusinessTrust class bank	Dec. 31, 2023	Dec. 31, 2024 USD ($)
Debt Instrument [Line Items]
Number of banks | bank	2
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 of New York
Debt Instrument [Line Items]
Collateral, at carrying cost	939		$ 769
Collateral, at fair value	939		571
Federal Home Loan Bank of New York
Debt Instrument [Line Items]
Collateral, at carrying cost	1,064		969
Collateral, at fair value	$ 948		$ 827