v3.25.1
Reconciliation of Total Revenue and Income Before Income Tax to Operating Revenue and Operating Income (Detail) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Segment Reporting, Revenue Reconciling Item    
Total Revenue $ 3,091.6 $ 3,200.3
Net Investment Loss (206.8) (1.2)
Operating Segments    
Segment Reporting, Revenue Reconciling Item    
Total Revenue 3,091.6 3,200.3
Net Investment Loss (206.8) (1.2)
Adjusted Operating Revenue 3,298.4 3,201.5
Income Before Income Tax 243.6 495.7
Adjusted Operating Income 466.8 514.5
Operating Segments | Long-term Care and Individual Disability Reinsurance Transaction    
Segment Reporting, Revenue Reconciling Item    
Net Investment Loss (175.9) 0.0
Operating Segments | Unrelated to Significant Transaction    
Segment Reporting, Revenue Reconciling Item    
Net Investment Loss (30.9) (1.2)
Operating Segments | Closed Block Individual Disability Reinsurance Transaction    
Segment Reporting, Revenue Reconciling Item    
Amortization of the Cost of Reinsurance (9.6) (10.4)
Non-Contemporaneous Reinsurance $ (6.8) $ (7.2)