Tax - Schedule of Components of Income Before Income Tax Expense (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
Mar. 31, 2024 |
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| Income before tax: | |||
| United Kingdom | $ 612.0 | $ 671.7 | $ 601.6 |
| Foreign Other | 48.4 | 45.8 | 55.1 |
| Income before tax | $ 660.4 | $ 717.5 | $ 656.7 |
| X | ||||||||||
- Definition The portion of earnings or loss from continuing operations before income taxes that is attributable to domestic operations. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition The portion of earnings or loss from continuing operations before income taxes that is attributable to foreign operations, which is defined as Income or Loss generated from operations located outside the entity's country of domicile. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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