Revenue Recognition (Tables)

12 Months Ended

Sep. 30, 2025

Revenue from Contract with Customer [Abstract]

Schedule of Revenues Disaggregated by Revenue Sources

The following tables present the Company’s revenues disaggregated by revenue sources:

	Fiscal Year Ended
	September 30, 2025		September 30, 2024		September 30, 2023
	(in millions)
Cost reimbursable	$	6,196.1	$	6,361.4	$	6,128.8
Guaranteed maximum price	5,960.7		6,030.0		4,887.7
Fixed price	3,982.8		3,714.1		3,362.0
Total revenue	$	16,139.6	$	16,105.5	$	14,378.5

	Fiscal Year Ended
	September 30, 2025		September 30, 2024		September 30, 2023
	(in millions)
Americas	$	12,526.4	$	12,487.0	$	10,976.4
Europe, Middle East, India, Africa	2,153.3		2,141.5		1,937.3
Asia-Australia-Pacific	1,459.9		1,477.0		1,464.8
Total revenue	$	16,139.6	$	16,105.5	$	14,378.5

Schedule of Net Accounts Receivable

Net accounts receivable consisted of the following:

	Fiscal Year Ended
	September 30, 2025		September 30, 2024
	(in millions)
Billed	$	1,934.3	$	2,184.9
Contract retentions	647.6		696.3
Total accounts receivable—gross	2,581.9		2,881.2
Allowance for doubtful accounts and credit losses	(84.8)		(87.9)
Total accounts receivable—net	$	2,497.1	$	2,793.3