Investments - Summary of Amortized Cost and Fair Values of Fixed Maturity Securities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Cost	$ 30.3	$ 31.0
Gross unrealized losses	(1.2)	(2.2)
Fair value	29.1	28.8
U.S. Treasury securities, obligations of U.S. Government agencies and Municipalities
Debt Securities, Available-for-sale [Line Items]
Cost	25.5	22.8
Gross unrealized losses	(1.1)	(1.8)
Fair value	24.4	21.0
Corporate debt
Debt Securities, Available-for-sale [Line Items]
Cost	4.8	8.2
Gross unrealized losses	(0.1)	(0.4)
Fair value	$ 4.7	$ 7.8