Securities, Securities with Unrealized Losses, Securities Pledged as Collateral and Holdings of Securities by One Issuer in Amount Greater Than 10% of Stockholders' Equity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Debt Securities Available-for-Sale [Abstract]
Securities of any one issuer, other than U.S. Government, exceeding 10% of stockholders' equity	$ 0.0	$ 0.0
Accrued interest receivable on securities	$ 1.2	$ 1.2
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]	Accrued interest receivable	Accrued interest receivable
Securities in nonaccrual status	$ 0.0	$ 0.0
Securities purchased with deterioration in credit quality	0.0	0.0
Collateral dependent securities	0.0	0.0
Securities Sold under Agreements to Repurchase [Member]
Debt Securities Available-for-Sale [Abstract]
Securities pledged as collateral	89.0	64.4
Federal Reserve for Borrowings under Bank Term Funding Program [Member]
Debt Securities Available-for-Sale [Abstract]
Securities pledged as collateral, at book value	107.3
Securities pledged as collateral	98.3
Asset Pledged as Collateral [Member] | Securities Sold under Agreements to Repurchase [Member]
Debt Securities Available-for-Sale [Abstract]
Securities pledged as collateral	89.0	64.4
Asset Pledged as Collateral [Member] | Public Deposits [Member]
Debt Securities Available-for-Sale [Abstract]
Securities pledged as collateral	0.0	0.0
U.S. Treasuries [Member] | Securities Sold under Agreements to Repurchase [Member]
Debt Securities Available-for-Sale [Abstract]
Securities pledged as collateral	47.8	19.2
U.S. Treasuries [Member] | Asset Pledged as Collateral [Member] | Securities Sold under Agreements to Repurchase [Member]
Debt Securities Available-for-Sale [Abstract]
Securities pledged as collateral	47.8	19.2
Federal Agency Debt [Member] | Securities Sold under Agreements to Repurchase [Member]
Debt Securities Available-for-Sale [Abstract]
Securities pledged as collateral	30.2	33.3
Federal Agency Debt [Member] | Asset Pledged as Collateral [Member] | Securities Sold under Agreements to Repurchase [Member]
Debt Securities Available-for-Sale [Abstract]
Securities pledged as collateral	30.2	33.3
Federal Agency Mortgage-backed Securities [Member] | Securities Sold under Agreements to Repurchase [Member]
Debt Securities Available-for-Sale [Abstract]
Securities pledged as collateral	11.0	11.9
Federal Agency Mortgage-backed Securities [Member] | Asset Pledged as Collateral [Member] | Securities Sold under Agreements to Repurchase [Member]
Debt Securities Available-for-Sale [Abstract]
Securities pledged as collateral	$ 11.0	$ 11.9