Earnings Per Share (Reconciliation Of Number Of Shares Used For Basic And Diluted Earnings Per Share ("EPS") Calculation ) (Details) - USD ($) $ / shares in Units, shares in Millions, $ 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
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income (Loss) Attributable to Parent	$ (2,414.0)		$ (119.1)		$ 97.0		$ 20.9		$ (2,259.3)		$ 136.9		$ 105.7		$ 95.1			$ (1,921.6)	$ 113.3
Weighted average number of shares outstanding																	448.0	458.0	466.7
Total shares and dilutive securities (in shares)																	448.0	458.0	468.3
Basic earnings per share attributable to TechnipFMC plc (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
Restricted Stock Units (RSUs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive effect of share-based payment arrangements (in shares)																		0.0	0.2
Performance shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive effect of share-based payment arrangements (in shares)																			1.4

[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.