v3.25.1
Length of Time Fixed Maturity Securities had been in a Gross Unrealized Loss Position (Detail) - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Debt Securities, Available-for-sale, Unrealized Loss Position    
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months $ 5,846.3 $ 7,031.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 210.5 269.9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 15,365.0 16,442.2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 2,690.6 3,044.1
United States Government and Government Agencies and Authorities    
Debt Securities, Available-for-sale, Unrealized Loss Position    
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months 46.0 43.7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 2.1 4.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 203.8 201.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 18.5 23.9
States, Municipalities, and Political Subdivisions    
Debt Securities, Available-for-sale, Unrealized Loss Position    
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months 261.4 425.8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 11.0 15.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 1,847.0 1,926.2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 487.7 554.4
Foreign Governments    
Debt Securities, Available-for-sale, Unrealized Loss Position    
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months 166.5 171.9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 10.6 10.6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 276.8 266.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 153.5 142.9
Public Utilities    
Debt Securities, Available-for-sale, Unrealized Loss Position    
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months 928.1 1,281.7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 39.4 48.4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 1,492.5 1,549.5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 282.9 316.0
Mortgage/Asset-backed Securities    
Debt Securities, Available-for-sale, Unrealized Loss Position    
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months [1] 233.3 199.9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss [1] 3.0 8.9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer [1] 285.8 285.9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss [1] 21.8 28.3
All Other Corporate Bonds    
Debt Securities, Available-for-sale, Unrealized Loss Position    
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months 4,207.0 4,904.4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 144.4 182.5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 11,255.3 12,209.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 1,725.9 1,978.3
Redeemable Preferred Stocks    
Debt Securities, Available-for-sale, Unrealized Loss Position    
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months 4.0 3.9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 0.0 0.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 3.8 3.7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss $ 0.3 $ 0.3
[1]
1Includes credit-tranched securities collateralized by loan obligations, auto loans, and other asset types