Stockholders' Equity (Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 5,044.1	$ 4,956.4	$ 5,296.2
Other comprehensive income (loss), net of tax	98.3	(15.3)	(375.7)
Ending balance	13,409.4	5,044.1	4,956.4
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(927.1)	(855.3)
Other comprehensive income (loss) before reclassifications, net of tax	(87.5)		(71.8)
Reclassification adjustment for net (gains) losses included in net income, net of tax	0.0		0.0
Other comprehensive income (loss), net of tax	(87.5)		(71.8)
Ending balance	(1,014.6)	(927.1)	(855.3)
Hedging
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(127.1)	(181.5)
Other comprehensive income (loss) before reclassifications, net of tax	53.7		(65.7)
Reclassification adjustment for net (gains) losses included in net income, net of tax	101.2		120.1
Other comprehensive income (loss), net of tax	154.9		54.4
Ending balance	27.8	(127.1)	(181.5)
Defined Pension and Other Post-Retirement Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(47.4)	(48.2)
Other comprehensive income (loss) before reclassifications, net of tax	43.2		7.0
Reclassification adjustment for net (gains) losses included in net income, net of tax	(12.7)		(6.2)
Other comprehensive income (loss), net of tax	30.5		0.8
Ending balance	(16.9)	(47.4)	(48.2)
Accumulated Other Comprehensive Loss Attributable to TechnipFMC plc
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(1,101.6)	(1,085.0)
Other comprehensive income (loss) before reclassifications, net of tax	9.4		(130.5)
Reclassification adjustment for net (gains) losses included in net income, net of tax	88.5		113.9
Other comprehensive income (loss), net of tax	97.9		(16.6)
Ending balance	(1,003.7)	(1,101.6)	(1,085.0)
Accumulated Other Comprehensive Loss Attributable to Non-controlling interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	0.2	(1.1)
Other comprehensive income (loss) before reclassifications, net of tax	0.4		1.3
Reclassification adjustment for net (gains) losses included in net income, net of tax	0.0		0.0
Other comprehensive income (loss), net of tax	0.4		1.3
Ending balance	$ 0.6	$ 0.2	$ (1.1)