Stockholders' Equity (Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	$ 10,388.9	$ 13,367.4
Other comprehensive income	37.4	13.4
Ending balance	10,373.6	$ 13,239.8
Foreign Currency Translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(1,234.4)
Other comprehensive income (loss) before reclassifications, net of tax	20.2
Other comprehensive income	20.2
Ending balance	(1,214.2)
Hedging
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(32.9)
Other comprehensive income (loss) before reclassifications, net of tax	16.0
Reclassification adjustment for net losses (gains) included in net income, net of tax	(0.3)
Other comprehensive income	15.7
Ending balance	(17.2)
Defined Pension and Other Post-Retirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(92.4)
Other comprehensive income (loss) before reclassifications, net of tax	0.5
Reclassification adjustment for net losses (gains) included in net income, net of tax	0.3
Other comprehensive income	0.8
Ending balance	(91.6)
Accumulated Other Comprehensive Loss attributable to TechnipFMC plc
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(1,359.7)
Other comprehensive income (loss) before reclassifications, net of tax	36.7
Other comprehensive income	36.7
Ending balance	(1,323.0)
Accumulated Other Comprehensive Loss attributable to Noncontrolling interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(4.0)
Other comprehensive income (loss) before reclassifications, net of tax	0.7
Other comprehensive income	0.7
Ending balance	$ (3.3)