Stockholders' Equity (Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance	$ 4,175.6	$ 10,380.4	$ 7,688.1	$ 10,388.9
Other comprehensive loss	38.2	(95.6)	(208.0)	(82.9)
Ending balance	4,233.7	$ 10,123.8	4,233.7	$ 10,123.8
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			(208.3)
Other comprehensive loss			(208.3)
Ending balance	(1,438.4)		(1,438.4)
Hedging
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance			(5.8)
Other comprehensive income (loss) before reclassifications, net of tax			(9.1)
Reclassification adjustment for net losses included in net income (loss), net of tax			8.7
Other comprehensive loss			(0.4)
Ending balance	(6.2)		(6.2)
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			(0.4)
Reclassification adjustment for net losses included in net income (loss), net of tax			7.5
Other comprehensive loss			7.1
Ending balance	(164.5)		(164.5)
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			(217.8)
Reclassification adjustment for net losses included in net income (loss), net of tax			16.2
Other comprehensive loss			(201.6)
Ending balance	(1,609.1)		(1,609.1)
Accumulated Other Comprehensive  Loss Attributable to Non-Controlling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance			(4.7)
Other comprehensive income (loss) before reclassifications, net of tax			(6.4)
Other comprehensive loss			(6.4)
Ending balance	$ (11.1)		$ (11.1)