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Commitments and Contingencies (Details) $ in Millions			1 Months Ended	3 Months Ended
	Jan. 23, 2017 USD ($)	Nov. 22, 2016 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016 USD ($) item	Sep. 30, 2016 USD ($)
Commitments and Contingencies
Number of affiliates for which inspections occurred on accounts and records by World Bank | item				2
DOE Hanford Nuclear Reservation
Commitments and Contingencies
Payments for legal settlements		$ 57.5
Net benefit of settlement		$ 35.0
DOE Hanford Nuclear Reservation | Subsequent Event
Commitments and Contingencies
Payments for legal settlements	$ 5.3
Standby Letters of Credit
Commitments and Contingencies
Contingency liability of general and professional liability insurance programs and for payment and performance guarantees				$ 464.9	$ 474.5
Surety Bond
Commitments and Contingencies
Surety bonds issued				3,600.0	$ 3,300.0
DOE Deactivation Demolition And Removal Project | URS Corporation | Washington Group International
Commitments and Contingencies
Projects costs, maximum				146.0
DOE Deactivation Demolition And Removal Project | Department of Energy
Commitments and Contingencies
Projects costs, minimum				106.0
DOE Deactivation Demolition And Removal Project | Department of Energy | URS Corporation | Washington Group International
Commitments and Contingencies
Projects costs, minimum				106.0
Projects costs, maximum				$ 146.0
Amount recovery (including additional Fees)			$ 103.0
Minimum cost to complete the project and promised amenities			$ 100.0

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