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Commitments and Contingencies (Details) - USD ($)					1 Months Ended		12 Months Ended
	May 24, 2018	Jul. 21, 2017	Jul. 03, 2017	Apr. 01, 2017	Sep. 30, 2017	Dec. 31, 2014	Sep. 30, 2018	Sep. 02, 2016
URS | Design build contractor
Commitments and Contingencies
Damages claimed, value	$ 11,900,000		$ 70,000,000	$ 8,200,000
AECOM USA, Inc. | Minimum | New York Department of Environmental Conservation
Commitments and Contingencies
Damages claimed, value					$ 100,000
Advatech LLC
Commitments and Contingencies
Percentage of ownership in joint venture							60.00%
Advatech LLC | Genco
Commitments and Contingencies
Damages claimed, value		$ 81,000,000
Invoice amount								$ 81,000,000
DOE Deactivation, Demolition, And Removal Project | Department of Energy | Maximum
Commitments and Contingencies
Cost-reimbursement at risk							$ 106,000,000
DOE Deactivation, Demolition, And Removal Project | WGI Ohio and DOE | Minimum
Commitments and Contingencies
Cost-reimbursement at risk							106,000,000
DOE Deactivation, Demolition, And Removal Project | WGI Ohio and DOE | Maximum
Commitments and Contingencies
Cost-reimbursement at risk							146,000,000
DOE Deactivation, Demolition, And Removal Project | WGI Ohio
Commitments and Contingencies
Claim to DOE, including additional fees						$ 103,000,000
Possible costs which may exceed contracted amounts						$ 100,000,000
DOE Deactivation, Demolition, And Removal Project | WGI Ohio | Minimum
Commitments and Contingencies
Cost-reimbursement at risk							146,000,000
AECOM-Canyon Equity Fund, L.P
Commitments and Contingencies
Capital commitments							$ 35,000,000
Term of capital commitments							10 years
Standby letter of credit
Commitments and Contingencies
Contingency liability							$ 515,100,000
Surety Bond
Commitments and Contingencies
Contingency liability							$ 5,300,000,000

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The percentage of ownership in joint venture.

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