Quarterly Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 3,726.8		$ 3,335.1		$ 3,434.2		$ 2,913.0		$ 3,323.0		$ 3,143.8		$ 2,960.9		$ 3,125.2		$ 13,409.1	$ 12,552.9	$ 15,056.9
Cost of sales	3,067.2		2,726.4		2,745.2		2,411.9		2,767.7		2,558.5		2,422.2		2,524.6
Net income (loss)	(2,430.3)		(115.3)		113.7		19.8		(2,246.5)		134.2		110.1		91.4		$ (2,412.1)	(1,910.8)	134.2
Net income (loss) attributable to TechnipFMC plc	$ (2,414.0)		$ (119.1)		$ 97.0		$ 20.9		$ (2,259.3)		$ 136.9		$ 105.7		$ 95.1			$ (1,921.6)	$ 113.3
Basic earnings (loss) per share (usd per share)	$ (5.40)	[1]	$ (0.27)	[1]	$ 0.22	[1]	$ 0.05	[1]	$ (5.00)	[1]	$ 0.30	[1]	$ 0.23	[1]	$ 0.20	[1]	$ (5.39)	$ (4.20)
Diluted earnings (loss) per share (usd per share)	$ (5.40)	[1]	$ (0.27)	[1]	$ 0.21	[1]	$ 0.05	[1]	$ (5.00)	[1]	$ 0.30	[1]	$ 0.23	[1]	$ 0.20	[1]	$ (5.39)	$ (4.20)	$ 0.24

[1] Basic and diluted earnings (loss) per share are computed independently for each of the quarters presented. Therefore, the sum of quarterly basic and diluted per share information may not equal annual basic and diluted earnings (loss) per share.