Investments- Carrying Amounts Of Equity Method Limited Partnership Interest (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Net Investment Income [Line Items]
Limited partnership interests	$ 1,138.8	$ 983.7	[1]
Commercial mortgage loan funds
Net Investment Income [Line Items]
Limited partnership interests	660.8	593.6
Real estate equity funds
Net Investment Income [Line Items]
Limited partnership interests	109.2	71.3
Private equity funds
Net Investment Income [Line Items]
Limited partnership interests	92.7	76.3
Infrastructure equity funds
Net Investment Income [Line Items]
Limited partnership interests	77.2	72.0
Infrastructure debt funds
Net Investment Income [Line Items]
Limited partnership interests	59.1	60.0
Other funds
Net Investment Income [Line Items]
Limited partnership interests	$ 139.8	$ 110.5

[1] Recast for the adoption of ASU 2018-12. See Note 1 of the Consolidated Financial Statements