Discontinued Operations - Financial Information of Discontinued Operations (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net earnings (loss) from Disc Ops		$ (5,872)	$ (2,071)	$ (139,110)	$ (299,021)
Net earnings (loss) from Disc Ops attributable to Fluor		(6,261)	(2,177)	(140,090)	(299,814)
Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue		399,631	404,509	1,285,184	1,292,625
Cost of revenue		389,661	402,279	1,255,221	1,290,636
Gross Profit		9,970	2,230	29,963	1,989
G&A		(6,046)	(16)	(8,552)	(79)
Impairment expense		(4,809)	0	(126,285)	(295,239)
Loss on sale of AMECO North America				(24,864)	0
Foreign currency gain (loss)		(1,041)	(791)	40	(2,099)
Operating profit (loss)		(1,926)	1,423	(129,698)	(295,428)
Interest (expense) income, net		(1,332)	(1,487)	(3,738)	(4,468)
Earnings (loss) before taxes from Disc Ops		(3,258)	(64)	(133,436)	(299,896)
Income tax expense (benefit)		2,614	2,007	5,674	(875)
Net earnings (loss) from Disc Ops		(5,872)	(2,071)	(139,110)	(299,021)
Less: Net earnings (loss) from Disc Ops attributable to NCI		389	106	980	793
Net earnings (loss) from Disc Ops attributable to Fluor		(6,261)	(2,177)	(140,090)	(299,814)
Discontinued Operations | Stork
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue		376,668	346,702	1,184,694	1,122,540
Cost of revenue		366,640	345,984	1,154,204	1,130,485
Gross Profit		10,028	718	30,490	(7,945)
G&A		(1,246)	0	(3,752)	0
Impairment expense		0	0	(73,200)	(195,239)
Loss on sale of AMECO North America				0	0
Foreign currency gain (loss)		(387)	(678)	(384)	(1,684)
Operating profit (loss)		8,395	40	(46,846)	(204,868)
Interest (expense) income, net		(1,159)	(1,473)	(3,768)	(4,494)
Earnings (loss) before taxes from Disc Ops		7,236	(1,433)	(50,614)	(209,362)
Income tax expense (benefit)		1,491	287	5,674	(4,537)
Net earnings (loss) from Disc Ops		5,745	(1,720)	(56,288)	(204,825)
Less: Net earnings (loss) from Disc Ops attributable to NCI		390	106	981	793
Net earnings (loss) from Disc Ops attributable to Fluor		5,355	(1,826)	(57,269)	(205,618)
Discontinued Operations | AMECO
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue		22,963	57,807	100,490	170,085
Cost of revenue		21,453	54,240	96,573	148,727
Gross Profit		1,510	3,567	3,917	21,358
G&A		(4,800)	(13)	(4,800)	(64)
Impairment expense		(4,809)	0	(53,085)	(100,000)
Loss on sale of AMECO North America	$ (25,000)			(24,864)	0
Foreign currency gain (loss)		(654)	(113)	424	(415)
Operating profit (loss)		(8,753)	3,441	(78,408)	(79,121)
Interest (expense) income, net		(173)	(14)	30	26
Earnings (loss) before taxes from Disc Ops		(8,926)	3,427	(78,378)	(79,095)
Income tax expense (benefit)		1,123	1,720	0	3,662
Net earnings (loss) from Disc Ops		(10,049)	1,707	(78,378)	(82,757)
Less: Net earnings (loss) from Disc Ops attributable to NCI		(1)	0	(1)	0
Net earnings (loss) from Disc Ops attributable to Fluor		(10,048)	1,707	(78,377)	(82,757)
Discontinued Operations | Other
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue		0	0	0	0
Cost of revenue		1,568	2,055	4,444	11,424
Gross Profit		(1,568)	(2,055)	(4,444)	(11,424)
G&A		0	(3)	0	(15)
Impairment expense		0	0	0	0
Loss on sale of AMECO North America				0	0
Foreign currency gain (loss)		0	0	0	0
Operating profit (loss)		(1,568)	(2,058)	(4,444)	(11,439)
Interest (expense) income, net		0	0	0	0
Earnings (loss) before taxes from Disc Ops		(1,568)	(2,058)	(4,444)	(11,439)
Income tax expense (benefit)		0	0	0	0
Net earnings (loss) from Disc Ops		(1,568)	(2,058)	(4,444)	(11,439)
Less: Net earnings (loss) from Disc Ops attributable to NCI		0	0	0	0
Net earnings (loss) from Disc Ops attributable to Fluor		$ (1,568)	$ (2,058)	$ (4,444)	$ (11,439)