v3.25.2
Investments - Components of Net Realized Gains (Losses) (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Gain (Loss) on Securities [Line Items]        
Gross realized gains on available-for-sale securities $ 27.0 $ 3.0 $ 81.0 $ 6.0
Gross realized gains on equity securities 4.0 0.0 41.0 12.0
Subtotal gross realized gains on security sales 31.0 3.0 122.0 18.0
Gross realized loss on available-for-sale securities (9.0) (225.0) (93.0) (380.0)
Gross realized loss on equity securities (3.0) (5.0) (9.0) (11.0)
Subtotal gross realized losses on security sales (12.0) (230.0) (102.0) (391.0)
Net realized gains (losses) on available-for-sale securities sales 18.0 (222.0) (12.0) (374.0)
Net realized gains (losses) on equity securities sales 1.0 (5.0) 32.0 1.0
Subtotal net realized gains (losses) on security sales 19.0 (227.0) 20.0 (373.0)
Hybrid securities 11.0 3.0 14.0 11.0
Equity securities 357.0 97.0 141.0 391.0
Subtotal net holding period gains (losses) 368.0 100.0 155.0 402.0
Total net realized gains (losses) on securities 387.0 (127.0) 175.0 29.0
U.S. government obligations        
Gain (Loss) on Securities [Line Items]        
Gross realized gains on available-for-sale securities 24.0 1.0 77.0 1.0
Gross realized loss on available-for-sale securities (1.0) (192.0) (78.0) (327.0)
Net realized gains (losses) on available-for-sale securities sales 23.0 (191.0) (1.0) (326.0)
State and local government obligations        
Gain (Loss) on Securities [Line Items]        
Gross realized loss on available-for-sale securities 0.0 0.0 (2.0) 0.0
Net realized gains (losses) on available-for-sale securities sales 0.0 0.0 (2.0) 0.0
Corporate and other debt securities        
Gain (Loss) on Securities [Line Items]        
Gross realized gains on available-for-sale securities 2.0 1.0 3.0 4.0
Gross realized loss on available-for-sale securities (2.0) (23.0) (3.0) (38.0)
Net realized gains (losses) on available-for-sale securities sales 0.0 (22.0) 0.0 (34.0)
Commercial mortgage-backed securities        
Gain (Loss) on Securities [Line Items]        
Gross realized loss on available-for-sale securities (6.0) (10.0) (10.0) (15.0)
Net realized gains (losses) on available-for-sale securities sales (6.0) (10.0) (10.0) (15.0)
Nonredeemable preferred stocks        
Gain (Loss) on Securities [Line Items]        
Gross realized gains on equity securities 0.0 0.0 2.0 0.0
Gross realized loss on equity securities (3.0) (5.0) (5.0) (11.0)
Net realized gains (losses) on equity securities sales (3.0) (5.0) (3.0) (11.0)
Common equities        
Gain (Loss) on Securities [Line Items]        
Gross realized gains on equity securities 4.0 0.0 39.0 12.0
Gross realized loss on equity securities 0.0 0.0 (4.0) 0.0
Net realized gains (losses) on equity securities sales 4.0 0.0 35.0 12.0
Residential mortgage-backed securities        
Gain (Loss) on Securities [Line Items]        
Gross realized gains on available-for-sale securities 1.0 1.0 1.0 1.0
Net realized gains (losses) on available-for-sale securities sales $ 1.0 $ 1.0 $ 1.0 $ 1.0