Investments - Carrying Amount of Equity Method Limited Partnership Interests (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Schedule of Equity Method Investments
Limited partnership interests	$ 1,045.4	$ 983.7
Commercial mortgage loan funds
Schedule of Equity Method Investments
Limited partnership interests	623.7	593.6
Private equity funds
Schedule of Equity Method Investments
Limited partnership interests	77.7	76.3
Infrastructure equity funds
Schedule of Equity Method Investments
Limited partnership interests	62.6	60.0
Real estate equity funds
Schedule of Equity Method Investments
Limited partnership interests	87.7	71.3
Infrastructure debt funds
Schedule of Equity Method Investments
Limited partnership interests	73.2	72.0
Other funds
Schedule of Equity Method Investments
Limited partnership interests	$ 120.5	$ 110.5