Investments- Carrying Amounts Of Equity Method Limited Partnership Interest (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Net Investment Income [Line Items]
Limited partnership interests (Carried under Fair Value Option, 2025 $0.0 and 2024, $28.9)	$ 1,100.6	$ 1,121.3
Commercial mortgage loan funds
Net Investment Income [Line Items]
Limited partnership interests (Carried under Fair Value Option, 2025 $0.0 and 2024, $28.9)	590.7	596.0
Real estate equity funds
Net Investment Income [Line Items]
Limited partnership interests (Carried under Fair Value Option, 2025 $0.0 and 2024, $28.9)	127.5	144.7
Private equity funds
Net Investment Income [Line Items]
Limited partnership interests (Carried under Fair Value Option, 2025 $0.0 and 2024, $28.9)	118.3	102.2
Infrastructure equity funds
Net Investment Income [Line Items]
Limited partnership interests (Carried under Fair Value Option, 2025 $0.0 and 2024, $28.9)	52.4	81.7
Infrastructure debt funds
Net Investment Income [Line Items]
Limited partnership interests (Carried under Fair Value Option, 2025 $0.0 and 2024, $28.9)	73.9	69.0
Other funds
Net Investment Income [Line Items]
Limited partnership interests (Carried under Fair Value Option, 2025 $0.0 and 2024, $28.9)	$ 137.8	$ 127.7