STOCKHOLDERS’ EQUITY (Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	$ 4,214.3	$ 7,688.1
Other comprehensive income (loss), net of tax	(36.9)	(305.3)
Ending balance	3,695.5	$ 4,084.8
Foreign Currency Translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(1,401.2)
Other comprehensive income (loss) before reclassifications, net of tax	(28.2)
Reclassification adjustment for net losses included in net income (loss), net of tax	0.0
Other comprehensive income (loss), net of tax	(28.2)
Spin-off of Technip Energies	241.2
Ending balance	(1,188.2)
Hedging
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	34.0
Other comprehensive income (loss) before reclassifications, net of tax	(14.5)
Reclassification adjustment for net losses included in net income (loss), net of tax	(2.7)
Other comprehensive income (loss), net of tax	(17.2)
Spin-off of Technip Energies	(19.7)
Ending balance	(2.9)
Defined Pension  and Other Post-Retirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(255.3)
Other comprehensive income (loss) before reclassifications, net of tax	3.5
Reclassification adjustment for net losses included in net income (loss), net of tax	4.9
Other comprehensive income (loss), net of tax	8.4
Spin-off of Technip Energies	37.2
Ending balance	(209.7)
Accumulated Other Comprehensive  Loss Attributable to TechnipFMC plc
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(1,622.5)
Other comprehensive income (loss) before reclassifications, net of tax	(39.2)
Reclassification adjustment for net losses included in net income (loss), net of tax	2.2
Other comprehensive income (loss), net of tax	(37.0)
Spin-off of Technip Energies	258.7
Ending balance	(1,400.8)
Accumulated Other Comprehensive  Loss Attributable to Non-Controlling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(4.1)
Other comprehensive income (loss) before reclassifications, net of tax	0.1
Reclassification adjustment for net losses included in net income (loss), net of tax	0.0
Other comprehensive income (loss), net of tax	0.1
Spin-off of Technip Energies	0.0
Ending balance	$ (4.0)