Commitments and Contingencies - Warranty Claims (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||||||
|---|---|---|---|---|---|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
Mar. 31, 2026 |
Mar. 31, 2025 |
Dec. 31, 2025 |
Sep. 30, 2025 |
Dec. 31, 2024 |
Sep. 30, 2024 |
|
| Movement in Standard Product Warranty Accrual [Roll Forward] | ||||||||
| Standard Product Warranty Accrual | $ 546.5 | $ 557.3 | $ 546.5 | $ 557.3 | $ 560.8 | $ 566.2 | $ 570.4 | $ 566.9 |
| Standard Product Warranty Accrual, Increase for Warranties Issued | 40.7 | 43.0 | 79.9 | 87.0 | ||||
| Standard Product Warranty Accrual, Increase (Decrease) for Preexisting Warranties | (37.4) | (27.0) | (59.6) | (38.0) | ||||
| Standard Product Warranty Accrual, Decrease for Payments | $ 17.6 | $ 29.1 | $ 40.0 | $ 58.6 | ||||