Investments - Carrying Amount of Equity Method Limited Partnership Interests (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Schedule of Equity Method Investments
Limited partnership interests	$ 1,119.3	$ 1,138.8
Commercial mortgage loan funds
Schedule of Equity Method Investments
Limited partnership interests	646.2	660.8
Real estate equity funds
Schedule of Equity Method Investments
Limited partnership interests	103.3	109.2
Private equity funds
Schedule of Equity Method Investments
Limited partnership interests	95.5	92.7
Infrastructure equity funds
Schedule of Equity Method Investments
Limited partnership interests	78.0	77.2
Infrastructure debt funds
Schedule of Equity Method Investments
Limited partnership interests	62.4	59.1
Other funds
Schedule of Equity Method Investments
Limited partnership interests	$ 133.9	$ 139.8