Investments - Carrying Amount of Equity Method Limited Partnership Interests (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Schedule of Equity Method Investments
Limited partnership interests	$ 1,087.2	$ 1,138.8
Commercial mortgage loan funds
Schedule of Equity Method Investments
Limited partnership interests	600.1	660.8
Real estate equity funds
Schedule of Equity Method Investments
Limited partnership interests	102.0	109.2
Private equity funds
Schedule of Equity Method Investments
Limited partnership interests	99.0	92.7
Infrastructure equity funds
Schedule of Equity Method Investments
Limited partnership interests	77.3	77.2
Infrastructure debt funds
Schedule of Equity Method Investments
Limited partnership interests	67.0	59.1
Other funds
Schedule of Equity Method Investments
Limited partnership interests	$ 141.8	$ 139.8