Stockholders' Equity (Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	$ 7,688.1	$ 10,388.9
Other comprehensive income	(305.3)	37.4
Ending balance	4,084.8	$ 10,373.6
Foreign Currency Translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(1,230.1)
Other comprehensive income (loss) before reclassifications, net of tax	(206.8)
Other comprehensive income	(206.8)
Ending balance	(1,436.9)
Hedging
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(5.8)
Other comprehensive income (loss) before reclassifications, net of tax	(89.3)
Reclassification adjustment for net losses (gains) included in net income (loss), net of tax	0.1
Other comprehensive income	(89.2)
Ending balance	(95.0)
Defined Pension and Other Post-Retirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(171.6)
Other comprehensive income (loss) before reclassifications, net of tax	(0.7)
Reclassification adjustment for net losses (gains) included in net income (loss), net of tax	2.5
Other comprehensive income	1.8
Ending balance	(169.8)
Accumulated Other Comprehensive Loss attributable to TechnipFMC plc
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(1,407.5)
Other comprehensive income (loss) before reclassifications, net of tax	(296.8)
Reclassification adjustment for net losses (gains) included in net income (loss), net of tax	2.6
Other comprehensive income	(294.2)
Ending balance	(1,701.7)
Accumulated Other Comprehensive Loss attributable to non-controlling interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(4.7)
Other comprehensive income (loss) before reclassifications, net of tax	(11.1)
Other comprehensive income	(11.1)
Ending balance	$ (15.8)