Revenue Recognition - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Passed through costs included in revenue and cost of sales	$ 8,600.0	$ 8,900.0	$ 7,700.0
Transaction price, allocated	19,700.0
Contract liabilities, revenue recognized	918.9	801.0
Significant claims recorded in contract assets and other non-current assets	400.0	180.0
Trade receivables sold with no financial and legal obligations	$ 268.2	$ 319.5
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation (as percent)	57.00%
Revenue, performance obligation expected timing of satisfaction period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, performance obligation expected timing of satisfaction period	2 years