Debt - Narrative (Details) $ in Millions	6 Months Ended
Jun. 30, 2026 USD ($) class subsidiaryBusinessTrust	Dec. 31, 2025 USD ($)
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	$ 938	$ 707
Collateral, at fair value	683	707
Federal Home Loan Bank of New York
Debt Instrument [Line Items]
Collateral, at carrying cost	1,100	948
Collateral, at fair value	$ 928	$ 948

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