STOCKHOLDERS’ EQUITY (Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	$ 3,629.3	$ 4,175.6	$ 4,214.3	$ 7,688.1
Other comprehensive income (loss), net of tax	(64.7)	38.2	(8.2)	(208.0)
Ending balance	3,519.4	4,233.7	3,519.4	4,233.7
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			(0.3)
Reclassification adjustment for net losses included in net income (loss), net of tax			0.0
Other comprehensive income (loss), net of tax			(0.3)
Spin-off of Technip Energies			253.5
Ending balance	(1,148.0)		(1,148.0)
Hedging
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance			34.0
Other comprehensive income (loss) before reclassifications, net of tax			(28.8)
Reclassification adjustment for net losses included in net income (loss), net of tax			3.3
Other comprehensive income (loss), net of tax			(25.5)
Spin-off of Technip Energies			(19.7)
Ending balance	(11.2)		(11.2)
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			4.4
Reclassification adjustment for net losses included in net income (loss), net of tax			14.7
Other comprehensive income (loss), net of tax			19.1
Spin-off of Technip Energies			37.2
Ending balance	(199.0)		(199.0)
Accumulated Other Comprehensive  Loss Attributable to TechnipFMC plc
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	(1,294.9)	(1,645.8)	(1,622.5)	(1,407.5)
Other comprehensive income (loss) before reclassifications, net of tax			(24.7)
Reclassification adjustment for net losses included in net income (loss), net of tax			18.0
Other comprehensive income (loss), net of tax	(63.3)	36.7	(6.7)	(201.6)
Spin-off of Technip Energies			271.0
Ending balance	(1,358.2)	$ (1,609.1)	(1,358.2)	$ (1,609.1)
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			(1.5)
Reclassification adjustment for net losses included in net income (loss), net of tax			0.0
Other comprehensive income (loss), net of tax			(1.5)
Spin-off of Technip Energies			0.0
Ending balance	$ (5.6)		$ (5.6)