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Investments (Narratives) (Details) - USD ($) $ in Millions | 9 Months Ended |
--- | --- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Mar. 31, 2024
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments [Abstract] |  |  |
Assets Held by Insurance Regulators | $ 20.2 |  | $ 23.1
Available-for-sale Securities [Abstract] |  |  |
Gross realized gains on sales of Treasuries | 318.6 | $ 448.9 |
Provision for Loan, Lease, and Other Losses [Abstract] |  |  |
Financing Receivable, Credit Loss, Expense (Reversal) | 2.0 | 0.4 |
Matured or Redeemed Securities |  |  |
Available-for-sale Securities [Abstract] |  |  |
Available for sale securities, gross realized losses | 0.5 | 1.1 |
Moving and Storage Treasuries |  |  |
Available-for-sale Securities [Abstract] |  |  |
Gross realized gains on sales of Treasuries | 73.0 | 225.0 |
Corporate securities [Member] |  |  |
Available-for-sale Securities [Abstract] |  |  |
Available for sale securities, realized gains | $ 2.3 | $ 1.5 |

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