Supplemental Information (Changes in Estimates) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Change in Accounting Estimate [Line Items]
Operating income (loss)	$ (2,097.1)	$ 790.6	$ (609.9)	$ (893.8)
Contracts accounted for under percentage of completion
Change in Accounting Estimate [Line Items]
Operating income (loss)	$ 20.0	$ (20.0)	$ 78.0	$ (63.0)