Supplemental Information (Changes in Estimates) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Change in Accounting Estimate [Line Items]
Operating income (loss)	$ 752.7	$ (2,328.0)	$ 1,487.2	$ (1,684.4)
Contracts accounted for under percentage of completion
Change in Accounting Estimate [Line Items]
Operating income (loss)	$ (25.0)	$ (15.0)	$ (58.0)	$ (45.0)