Supplemental Information (Changes in Estimates) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Change in Accounting Estimate [Line Items]
Operating income (loss)	$ 790.6	$ 737.6	$ (893.8)	$ 2,041.7
Contracts accounted for under percentage of completion
Change in Accounting Estimate [Line Items]
Operating income (loss)	$ (20.0)	$ (50.0)	$ (63.0)	$ (115.0)