Basis of Presentation and Significant Accounting Policies - Schedule of Changes in MRBs due to Adoption of ASU 2018-12 (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Market risk benefit	$ 1.3	$ 0.2	$ 4.0	$ 4.8	$ 8.6
Less: Reinsurance recoverable					0.0
Market risk benefits	$ 38.3		$ 20.2		8.6
Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Market risk benefit					0.1
Adjustment for the difference between carrying amount and fair value, except for the difference due to instrument-specific credit risk
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Market risk benefit					6.8
Adjustment for cumulative effect of changes in the instrument-specific credit risk at issuance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Market risk benefit					1.7
Total adjustment for the difference between carrying amount and fair value
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Market risk benefit					$ 8.5