Investments - Available-for-sale Securities with Cost Basis in Excess of Fair Value - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Investments Debt And Equity Securities [Abstract]
Available-for-sale fixed-maturities with cost basis in excess of fair values, cost basis	$ 2,575,400.0		$ 2,713.8
Available-for-sale credit (gains) losses	$ 2.2	$ (0.1)