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Partnerships and Joint Ventures - Ownership and Receivables (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
COOEC Fluor Heavy Industries Co., Ltd.
Variable interest entity information
Capital contribution	$ 26
COOEC Fluor Heavy Industries Co., Ltd.
Variable interest entity information
Ownership percentage		49.00%
SACYR \| Discontinued Operations, Disposed of by Sale \| Urban Solutions
Variable interest entity information
Ownership percentage		10.00%
Loss on sale of investment		$ 20
SACYR \| Discontinued Operations, Disposed of by Sale \| Energy & Chemicals
Variable interest entity information
Ownership percentage			50.00%
Loss on sale of investment			$ 11
Accounts and notes receivable, net \| Variable Interest Entity, Not Primary Beneficiary
Variable interest entity information
Receivables related to work performed for unconsolidated partnerships and joint ventures		$ 216		$ 207
Partnership \| Minority Interest Ownership Percentage by Parent \| Majority
Variable interest entity information
Entity's interest in partnership or joint venture (as a percent)		50.00%