v3.26.1
Investments - Components of Net Realized Gains (Losses) (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Gain (Loss) on Securities [Line Items]        
Gross realized gains on available-for-sale securities $ 60.0 $ 27.0 $ 187.0 $ 81.0
Gross realized gains on equity securities 25.0 4.0 46.0 41.0
Subtotal gross realized gains on security sales 85.0 31.0 233.0 122.0
Gross realized loss on available-for-sale securities (59.0) (9.0) (100.0) (93.0)
Gross realized loss on equity securities (10.0) (3.0) (21.0) (9.0)
Subtotal gross realized losses on security sales (69.0) (12.0) (121.0) (102.0)
Net realized gains (losses) on available-for-sale securities sales 1.0 18.0 87.0 (12.0)
Net realized gains (losses) on equity securities sales 15.0 1.0 25.0 32.0
Subtotal net realized gains (losses) on security sales 16.0 19.0 112.0 20.0
Hybrid securities 17.0 11.0 (10.0) 14.0
Equity securities 571.0 357.0 382.0 141.0
Subtotal net holding period gains (losses) 588.0 368.0 372.0 155.0
Total net realized gains (losses) on securities 604.0 387.0 484.0 175.0
U.S. government        
Gain (Loss) on Securities [Line Items]        
Gross realized gains on available-for-sale securities 51.0 24.0 150.0 77.0
Gross realized loss on available-for-sale securities (49.0) (1.0) (85.0) (78.0)
Net realized gains (losses) on available-for-sale securities sales 2.0 23.0 65.0 (1.0)
State and local government        
Gain (Loss) on Securities [Line Items]        
Gross realized gains on available-for-sale securities 0.0 0.0 1.0 0.0
Gross realized loss on available-for-sale securities (4.0) 0.0 (4.0) (2.0)
Net realized gains (losses) on available-for-sale securities sales (4.0) 0.0 (3.0) (2.0)
Corporate and other debt        
Gain (Loss) on Securities [Line Items]        
Gross realized gains on available-for-sale securities 9.0 2.0 35.0 3.0
Gross realized loss on available-for-sale securities (6.0) (2.0) (11.0) (3.0)
Net realized gains (losses) on available-for-sale securities sales 3.0 0.0 24.0 0.0
Residential mortgage-backed        
Gain (Loss) on Securities [Line Items]        
Gross realized gains on available-for-sale securities 0.0 1.0 1.0 1.0
Net realized gains (losses) on available-for-sale securities sales 0.0 1.0 1.0 1.0
Commercial mortgage-backed        
Gain (Loss) on Securities [Line Items]        
Gross realized loss on available-for-sale securities 0.0 (6.0) 0.0 (10.0)
Net realized gains (losses) on available-for-sale securities sales 0.0 (6.0) 0.0 (10.0)
Nonredeemable preferred stocks        
Gain (Loss) on Securities [Line Items]        
Gross realized gains on equity securities 2.0 0.0 10.0 2.0
Gross realized loss on equity securities (3.0) (3.0) (8.0) (5.0)
Net realized gains (losses) on equity securities sales (1.0) (3.0) 2.0 (3.0)
Common equities        
Gain (Loss) on Securities [Line Items]        
Gross realized gains on equity securities 23.0 4.0 36.0 39.0
Gross realized loss on equity securities (7.0) 0.0 (13.0) (4.0)
Net realized gains (losses) on equity securities sales $ 16.0 $ 4.0 $ 23.0 $ 35.0