Quarterly Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2020		Sep. 30, 2020		Jun. 30, 2020		Mar. 31, 2020		Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 3,426.1		$ 3,335.7		$ 3,158.5		$ 3,130.3		$ 3,726.8		$ 3,335.1		$ 3,434.2		$ 2,913.0		$ 13,050.6	$ 13,409.1	$ 12,552.9
Cost of sales	2,973.8		2,882.3		2,647.0		2,706.3		3,067.2		2,726.4		2,745.2		2,411.9
Net income (loss)	(13.9)		6.4		15.3		(3,245.7)		(2,430.3)		(115.3)		113.7		19.8		$ (3,237.9)	(2,412.1)	(1,910.8)
Net income (loss) attributable to TechnipFMC plc	$ (39.3)		$ (3.9)		$ 11.7		$ (3,256.1)		$ (2,414.0)		$ (119.1)		$ 97.0		$ 20.9			$ (2,415.2)	$ (1,921.6)
Basic earnings (loss) per share (usd per share)	$ (0.09)	[1]	$ (0.01)	[1]	$ 0.03	[1]	$ (7.28)	[1]	$ (5.40)	[1]	$ (0.27)	[1]	$ 0.22	[1]	$ 0.05	[1]	$ (7.33)	$ (5.39)
Diluted earnings (loss) per share (usd per share)	$ (0.09)	[1]	$ (0.01)	[1]	$ 0.03	[1]	$ (7.28)	[1]	$ (5.40)	[1]	$ (0.27)	[1]	$ 0.21	[1]	$ 0.05	[1]	$ (7.33)	$ (5.39)	$ (4.20)

[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.