Derivatives (Narratives) (Details) - USD ($) $ in Millions |
6 Months Ended | |
|---|---|---|
Sep. 30, 2025 |
Sep. 30, 2024 |
|
| AOCI Attributable to Parent [Abstract] | ||
| Investment Income, Net | $ 5.9 | $ 6.5 |
| Decrease, fair value, cash flow hedges | ||
| AOCI Attributable to Parent [Abstract] | ||
| Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments | 4.4 | 0.2 |
| Reclassified AOCI | ||
| AOCI Attributable to Parent [Abstract] | ||
| Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments | 3.6 | $ 8.2 |
| Reclassification net gains Interest Rate Contracts | ||
| AOCI Attributable to Parent [Abstract] | ||
| Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments | $ 2.5 | |