Investments- Carrying Amounts Of Equity Method Limited Partnership Interest (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Net Investment Income [Line Items]
Limited partnership interests (Carried under Fair Value Option, 2024 $28.9 and 2023, $29.5)	$ 1,121.3	$ 1,138.8
Commercial mortgage loan funds
Net Investment Income [Line Items]
Limited partnership interests (Carried under Fair Value Option, 2024 $28.9 and 2023, $29.5)	596.0	660.8
Real estate equity funds
Net Investment Income [Line Items]
Limited partnership interests (Carried under Fair Value Option, 2024 $28.9 and 2023, $29.5)	144.7	109.2
Private equity funds
Net Investment Income [Line Items]
Limited partnership interests (Carried under Fair Value Option, 2024 $28.9 and 2023, $29.5)	102.2	92.7
Infrastructure equity funds
Net Investment Income [Line Items]
Limited partnership interests (Carried under Fair Value Option, 2024 $28.9 and 2023, $29.5)	81.7	77.2
Infrastructure debt funds
Net Investment Income [Line Items]
Limited partnership interests (Carried under Fair Value Option, 2024 $28.9 and 2023, $29.5)	69.0	59.1
Other funds
Net Investment Income [Line Items]
Limited partnership interests (Carried under Fair Value Option, 2024 $28.9 and 2023, $29.5)	$ 127.7	$ 139.8