Supplemental Information (Changes in Estimates) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Change in Accounting Estimate [Line Items]
Operating income (loss)	$ 637.2	$ 459.8	$ 1,304.1	$ 1,111.8
Contracts accounted for under percentage of completion
Change in Accounting Estimate [Line Items]
Operating income (loss)	$ (35.0)	$ (35.0)	$ (65.0)	$ (60.0)