v3.26.1
Shareholders' Equity - Schedule of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Reclassification adjustments, included in net income $ (7.6) $ 42.5 $ 3.7
Unrealized gains/ (losses) on AFS debt securities [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning balance (21.7) (41.7) (8.5)
Increase/(decrease) 18.1 (22.5) (36.9)
Reclassification adjustments, included in net income (7.6) 42.5 3.7
Total increase/(decrease) 10.5 20.0 (33.2)
Ending balance (11.2) (21.7) (41.7)
Foreign currency translation gains/ (losses) [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning balance 3.5 (17.3) (28.2)
Increase/(decrease) 59.8 20.8 10.9
Reclassification adjustments, included in net income 0.0 0.0 0.0
Total increase/(decrease) 59.8 20.8 10.9
Ending balance 63.3 3.5 (17.3)
Tax (expense)/ benefit [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning balance 7.0 12.2 3.6
Increase/(decrease) (2.6) (5.2) 8.6
Reclassification adjustments, included in net income 0.0 0.0 0.0
Total increase/(decrease) (2.6) (5.2) 8.6
Ending balance 4.4 7.0 12.2
Accumulated Other Comprehensive Income [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning balance (11.2) (46.8) (33.1)
Increase/(decrease) 75.3 (6.9) (17.4)
Reclassification adjustments, included in net income (7.6) 42.5 3.7
Total increase/(decrease) 67.7 35.6 (13.7)
Ending balance $ 56.5 $ (11.2) $ (46.8)