Commitments and Contingencies - Legal Claims and Insurance (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | |||
|---|---|---|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
Mar. 31, 2026 |
Mar. 31, 2025 |
Sep. 30, 2025 |
|
| Rollforward of reserves for legal claims | |||||
| Reserves for legal claims, beginning of period | $ 1,122.8 | $ 939.1 | $ 1,143.6 | $ 949.6 | |
| Increase in reserves | 27.0 | 66.7 | 50.3 | 72.5 | |
| Payments | (13.1) | (14.5) | (57.2) | (30.8) | |
| Reserves for legal claims, end of period | $ 1,136.7 | 991.3 | $ 1,136.7 | 991.3 | |
| Construction Defect Portion of Loss Contingency Accrual | 99.00% | 99.00% | 98.00% | ||
| Litigation Settlement, Expense | $ 58.0 | 97.3 | |||
| Insurance receivables | $ 152.3 | $ 126.7 | $ 152.3 | $ 126.7 | $ 167.0 |