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Commitments and Contingencies (Details) - USD ($) $ in Millions					1 Months Ended		3 Months Ended	12 Months Ended
	Oct. 31, 2019	May 24, 2018	Jul. 03, 2017	Apr. 01, 2017	Apr. 30, 2019	Dec. 31, 2014	Oct. 01, 2019	Sep. 30, 2019	Apr. 25, 2019	Mar. 31, 2019	Mar. 26, 2019	Feb. 28, 2019
URS | Design build contractor
Commitments and Contingencies
Damages claimed, value		$ 11.9	$ 70.0	$ 8.2
Advatech LLC | Genco
Commitments and Contingencies
Damages claimed, value					$ 132.0
Department of Energy Deactivation, Demolition, and Removal Project | Department of Energy
Commitments and Contingencies
Cost-reimbursement at risk								$ 106.0
Department of Energy Deactivation, Demolition, and Removal Project | AECOM E&C and DOE
Commitments and Contingencies
Cost-reimbursement at risk								146.0
Department of Energy Deactivation, Demolition, and Removal Project | AECOM E&C and DOE | Minimum
Commitments and Contingencies
Cost-reimbursement at risk								106.0
Department of Energy Deactivation, Demolition, and Removal Project | AECOM E&C
Commitments and Contingencies
Cost-reimbursement at risk								146.0
Claim to DOE, including additional fees						$ 103.0
Possible costs which may exceed contracted amounts						$ 100.0
Refinery Turnaround Project | AECOM E&C
Commitments and Contingencies
Damages claimed, value	$ 144.0
Recoverable from refinery owner								90.0				$ 90.0
Loss contingency, receivable amount									$ 132.0	$ 79.0	$ 79.0
AECOM-Canyon Equity Fund, L.P
Commitments and Contingencies
Capital commitments								$ 35.0
Term (in years)								10 years
URS | Design build contractor
Commitments and Contingencies
Damages claimed, value							$ 103.7
Damage claimed							4.9
Amount awarded							4.9
Amount awarded to contractor							$ 2.7
Standby letter of credit
Commitments and Contingencies
Contingency liability								$ 493.7
Surety Bond
Commitments and Contingencies
Contingency liability								$ 4,800.0

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