v3.26.1
Accumulated Other Comprehensive Income (Loss) - Other Comprehensive Income (Loss) Reclassification Adjustments (Detail) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Mar. 31, 2026
Jun. 30, 2025
Mar. 31, 2025
Jun. 30, 2026
Jun. 30, 2025
Accumulated Other Comprehensive Income Loss [Line Items]            
Pretax change before reclassifications $ (35.0)   $ 55.6   $ (119.8) $ 182.4
Reclassifications out of AOCI 2.0   5.8   3.8 7.8
Tax effect 7.5   (7.2)   24.7 (39.4)
Total other comprehensive (loss) income, net of tax (25.5) $ (65.8) 54.2 $ 96.6 (91.3) 150.8
Unrealized Gains (Losses) on Debt Securities            
Accumulated Other Comprehensive Income Loss [Line Items]            
Pretax change before reclassifications (27.7)   19.9   (100.1) 142.8
Reclassifications out of AOCI 1.5   5.4   2.8 6.9
Tax effect 7.6   (6.3)   24.7 (38.4)
Total other comprehensive (loss) income, net of tax (18.6)   19.0   (72.6) 111.3
Foreign Currency Translation Adjustment            
Accumulated Other Comprehensive Income Loss [Line Items]            
Pretax change before reclassifications (7.3)   35.7   (19.7) 39.6
Reclassifications out of AOCI 0.0   0.0   0.0 0.0
Tax effect 0.1   (0.8)   0.3 (0.8)
Total other comprehensive (loss) income, net of tax (7.2)   34.9   (19.4) 38.8
Pension Benefit Adjustment            
Accumulated Other Comprehensive Income Loss [Line Items]            
Pretax change before reclassifications 0.0   0.0   0.0 0.0
Reclassifications out of AOCI 0.5   0.4   1.0 0.9
Tax effect (0.2)   (0.1)   (0.3) (0.2)
Total other comprehensive (loss) income, net of tax $ 0.3   $ 0.3   $ 0.7 $ 0.7