v3.26.1
Schedule I - Investments (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Fair Value $ 6,393.6  
Amount at which shown at the balance sheet 6,568.6  
Privately-held Investments [1] 121.8 $ 286.8
Other Investments [2] 279.6 267.2
Fair Value, Recurring [Member] | Apollo originating partnership    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Privately-held Investments 4.8  
Fair Value, Recurring [Member] | Apollo real estate fund    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Other Investments 81.4  
Fair Value, Recurring [Member] | Apollo originating partnership    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Privately-held Investments 4.8 $ 73.6
U.S. government    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 1,465.6  
Fair Value 1,485.9  
Amount at which shown at the balance sheet 1,485.9  
U.S. agency    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 2.0  
Fair Value 2.0  
Amount at which shown at the balance sheet 2.0  
Municipal    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 95.6  
Fair Value 97.0  
Amount at which shown at the balance sheet 97.0  
Corporate    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 2,136.6  
Fair Value 2,138.8  
Amount at which shown at the balance sheet 2,138.8  
High yield loans    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 99.6  
Fair Value 100.0  
Amount at which shown at the balance sheet 100.0  
Non-U.S. government-backed corporate    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 66.0  
Fair Value 66.3  
Amount at which shown at the balance sheet 66.3  
Non-U.S. government    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 438.2  
Fair Value 439.2  
Amount at which shown at the balance sheet 439.2  
Asset-backed    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 873.0  
Fair Value 872.9  
Amount at which shown at the balance sheet 961.7  
Asset-backed | Fair Value, Recurring [Member] | Apollo originating partnership    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Other Investments 88.8  
Non-agency commercial mortgage-backed securities    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 9.8  
Fair Value 9.5  
Amount at which shown at the balance sheet 9.5  
Agency mortgage-backed    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 774.1  
Fair Value 753.2  
Amount at which shown at the balance sheet 753.2  
Fixed maturities    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 5,960.5  
Fair Value 5,964.8  
Amount at which shown at the balance sheet 6,053.6  
Short-term investments — Available for sale    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 45.4  
Fair Value 45.4  
Amount at which shown at the balance sheet 45.4  
Privately-held investments    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 170.7  
Fair Value 167.5  
Amount at which shown at the balance sheet 172.3  
Equity Method Investments    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Fair Value 9.6  
Amount at which shown at the balance sheet 9.6  
Other investments    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Fair Value 198.2  
Amount at which shown at the balance sheet 279.6  
Equity investments    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Fair Value $ 8.1  
[1] Privately-held investments, trading at fair value include related party investments totaling $4.8 million (2024 — $73.6 million).
[2] Other investments includes related party investments of $81.4 million (2024 — $78.6 million).