v3.26.1
Investments - Components of Net Realized Gains (Losses) (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Gain (Loss) on Securities [Line Items]    
Gross realized gains on available-for-sale securities $ 127.0 $ 54.0
Gross realized gains on equity securities 21.0 37.0
Subtotal gross realized gains on security sales 148.0 91.0
Gross realized loss on available-for-sale securities (41.0) (84.0)
Gross realized loss on equity securities (11.0) (6.0)
Subtotal gross realized losses on security sales (52.0) (90.0)
Net realized gains (losses) on available-for-sale securities sales 86.0 (30.0)
Net realized gains (losses) on equity securities sales 10.0 31.0
Subtotal net realized gains (losses) on security sales 96.0 1.0
Hybrid securities (27.0) 3.0
Equity securities (189.0) (216.0)
Subtotal net holding period gains (losses) (216.0) (213.0)
Total net realized gains (losses) on securities (120.0) (212.0)
U.S. government    
Gain (Loss) on Securities [Line Items]    
Gross realized gains on available-for-sale securities 99.0 53.0
Gross realized loss on available-for-sale securities (36.0) (77.0)
Net realized gains (losses) on available-for-sale securities sales 63.0 (24.0)
State and local government    
Gain (Loss) on Securities [Line Items]    
Gross realized gains on available-for-sale securities 1.0 0.0
Gross realized loss on available-for-sale securities 0.0 (2.0)
Net realized gains (losses) on available-for-sale securities sales 1.0 (2.0)
Corporate and other debt    
Gain (Loss) on Securities [Line Items]    
Gross realized gains on available-for-sale securities 26.0 1.0
Gross realized loss on available-for-sale securities (5.0) (1.0)
Net realized gains (losses) on available-for-sale securities sales 21.0 0.0
Residential mortgage-backed    
Gain (Loss) on Securities [Line Items]    
Gross realized gains on available-for-sale securities 1.0 0.0
Net realized gains (losses) on available-for-sale securities sales 1.0 0.0
Commercial mortgage-backed    
Gain (Loss) on Securities [Line Items]    
Gross realized loss on available-for-sale securities 0.0 (4.0)
Net realized gains (losses) on available-for-sale securities sales 0.0 (4.0)
Nonredeemable preferred stocks    
Gain (Loss) on Securities [Line Items]    
Gross realized gains on equity securities 8.0 2.0
Gross realized loss on equity securities (5.0) (2.0)
Net realized gains (losses) on equity securities sales 3.0 0.0
Common equities    
Gain (Loss) on Securities [Line Items]    
Gross realized gains on equity securities 13.0 35.0
Gross realized loss on equity securities (6.0) (4.0)
Net realized gains (losses) on equity securities sales $ 7.0 $ 31.0