v3.26.3
Derivative Financial Instruments - Credit Derivatives Sold (Details) - USD ($)
$ in Millions
 9 Months Ended 12 Months Ended
Sep. 30, 2026
Dec. 31, 2025
Credit derivatives sold disclosures    
Notional amount $ 1,116.9 $ 946.0
Fair value 11.4 16.1
Maximum future payments $ 1,116.9 $ 946.0
Weighted average expected life 12 years 4 months 24 days 13 years 8 months 12 days
Single name credit default swaps    
Credit derivatives sold disclosures    
Notional amount $ 616.9 $ 446.0
Fair value (1.8) 0.1
Maximum future payments $ 616.9 $ 446.0
Weighted average expected life 5 years 10 months 24 days 5 years 3 months 18 days
Single name credit default swaps | Corporate debt securities | AA    
Credit derivatives sold disclosures    
Notional amount $ 207.6 $ 96.7
Fair value 1.2 1.0
Maximum future payments $ 207.6 $ 96.7
Weighted average expected life 7 years 6 months 6 years 4 months 24 days
Single name credit default swaps | Corporate debt securities | A    
Credit derivatives sold disclosures    
Notional amount $ 219.3 $ 219.3
Fair value (4.0) (3.2)
Maximum future payments $ 219.3 $ 219.3
Weighted average expected life 6 years 6 months 7 years 2 months 12 days
Single name credit default swaps | Corporate debt securities | BBB    
Credit derivatives sold disclosures    
Notional amount $ 190.0 $ 130.0
Fair value 1.0 2.3
Maximum future payments $ 190.0 $ 130.0
Weighted average expected life 3 years 6 months 1 year 6 months
Single name total return swaps    
Credit derivatives sold disclosures    
Notional amount $ 500.0 $ 500.0
Fair value 13.2 16.0
Maximum future payments $ 500.0 $ 500.0
Weighted average expected life 20 years 4 months 24 days 21 years 1 month 6 days
Single name total return swaps | Government/municipalities | AAA    
Credit derivatives sold disclosures    
Notional amount $ 40.0 $ 40.0
Fair value 0.9 1.2
Maximum future payments $ 40.0 $ 40.0
Weighted average expected life 28 years 9 months 18 days 29 years 7 months 6 days
Single name total return swaps | Government/municipalities | AA    
Credit derivatives sold disclosures    
Notional amount $ 195.0 $ 195.0
Fair value 2.1 3.5
Maximum future payments $ 195.0 $ 195.0
Weighted average expected life 19 years 8 months 12 days 20 years 6 months
Single name total return swaps | Government/municipalities | A    
Credit derivatives sold disclosures    
Notional amount $ 210.0 $ 210.0
Fair value 8.6 9.5
Maximum future payments $ 210.0 $ 210.0
Weighted average expected life 20 years 10 months 24 days 21 years 7 months 6 days
Single name total return swaps | Government/municipalities | BBB    
Credit derivatives sold disclosures    
Notional amount $ 55.0 $ 55.0
Fair value 1.6 1.8
Maximum future payments $ 55.0 $ 55.0
Weighted average expected life 14 years 6 months 15 years 3 months 18 days