Revenue - Impact on Primary Financial Statements (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Revenue:
Lease and other revenue	$ 53.3	$ 55.9	$ 102.7	$ 89.6
Total revenue	2,960.9	3,845.0	6,086.1	7,233.0
Costs and expenses
Cost of service revenue	1,846.9	2,509.5	3,799.4	4,887.1
Cost of product revenue	544.1	614.8	1,078.9	1,192.5
Cost of lease and other revenue	31.2	37.7	68.5	62.7
Selling, general and administrative expense	281.4	268.0	584.5	522.1
Research and development expense	53.6	49.1	94.7	92.5
Impairment, restructuring and other expenses (Note 14)	11.4	(12.3)	22.9	(2.6)
Merger transaction and integration costs (Note 2)	9.0	23.3	14.6	78.0
Total costs and expenses	2,777.6	3,490.1	5,663.5	6,832.3
Other income (expense), net	2.2	(50.3)	(23.0)	13.2
Income from equity affiliates (Note 9)	40.2	12.7	54.2	22.1
Income before net interest expense and income taxes	225.7	317.3	453.8	436.0
Net interest expense	(50.9)	(72.1)	(138.3)	(154.2)
Income before income taxes	174.8	245.2	315.5	281.8
Provision for income taxes (Note 16)	64.7	86.2	114.0	138.0
Net income	110.1	159.0	201.5	143.8
Net (income) loss attributable to noncontrolling interests	(4.4)	5.9	(0.7)	2.4
Net income attributable to TechnipFMC plc	105.7	164.9	200.8	146.2
Assets
Cash and cash equivalents	5,555.4	7,179.1	5,555.4	7,179.1	$ 6,737.4	$ 6,269.3
Trade receivables, net	2,198.6		2,198.6		1,484.4
Contract assets	1,412.9		1,412.9		1,755.5
Inventories, net (Note 7)	1,085.6		1,085.6		987.0
Derivative financial instruments (Note 17)	83.9		83.9		78.3
Income taxes receivable	338.7		338.7		337.0
Advances paid to suppliers	300.0		300.0		391.3
Other current assets (Note 8)	866.4		866.4		1,206.2
Total current assets	11,841.5		11,841.5		12,977.1
Investments in equity affiliates	346.6		346.6		272.5
Property, plant and equipment, net of accumulated depreciation	3,697.8		3,697.8		3,871.5
Goodwill	9,009.8		9,009.8		8,929.8
Intangible assets, net of accumulated amortization	1,253.8		1,253.8		1,333.8
Deferred income taxes	442.0		442.0		454.7
Derivative financial instruments (Note 17)	84.6		84.6		94.9
Other assets	382.4		382.4		329.4
Total assets	27,058.5		27,058.5		28,263.7
Liabilities and equity
Less: current borrowings	78.5		78.5		77.1
Accounts payable, trade	2,924.6		2,924.6		3,958.7
Contract liabilities	3,973.3		3,973.3		3,314.2
Accrued payroll	350.7		350.7		402.2
Derivative financial instruments (Note 17)	97.9		97.9		69.0
Income taxes payable	255.3		255.3		320.3
Other current liabilities (Note 8)	1,477.4		1,477.4		1,687.9
Total current liabilities	9,157.7		9,157.7		9,829.4
Long-term debt, less current portion (Note 11)	3,787.5		3,787.5		3,777.9
Accrued pension and other post-retirement benefits, less current portion	242.4		242.4		282.0
Derivative financial instruments (Note 17)	88.3		88.3		68.1
Deferred income taxes	355.8		355.8		419.7
Other liabilities	379.2		379.2		477.2
Commitments and contingent liabilities (Note 15)
Redeemable noncontrolling interest	39.7		39.7
Stockholders’ equity (Note 12)
Ordinary shares	457.5		457.5		465.1
Ordinary shares held in employee benefit trust	(3.9)		(3.9)		(4.8)
Capital in excess of par value of ordinary shares	10,335.5		10,335.5		10,483.3
Retained earnings	3,376.5		3,376.5		3,448.0
Accumulated other comprehensive loss	(1,180.1)		(1,180.1)		(1,003.7)
Total TechnipFMC plc stockholders’ equity	12,985.5		12,985.5		13,387.9
Noncontrolling interests	22.4		22.4		21.5
Total equity	13,007.9		13,007.9		13,409.4
Total liabilities and equity	27,058.5		27,058.5		$ 28,263.7
Difference between revenue guidance in effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue:
Total revenue	47.1		10.9
Costs and expenses
Cost of service revenue	(4.8)		(18.7)
Cost of product revenue	2.1		(0.9)
Total costs and expenses	(2.7)		(19.6)
Income before net interest expense and income taxes	49.8		30.5
Income before income taxes	49.8		30.5
Provision for income taxes (Note 16)	18.4		13.2
Net income	31.4		17.3
Net (income) loss attributable to noncontrolling interests	(0.6)		(0.5)
Net income attributable to TechnipFMC plc	30.8		16.8
Assets
Trade receivables, net	(1,116.4)		(1,116.4)
Contract assets	409.9		409.9
Inventories, net (Note 7)	25.0		25.0
Income taxes receivable	0.1		0.1
Total current assets	(681.4)		(681.4)
Deferred income taxes	(23.1)		(23.1)
Other assets	(1.0)		(1.0)
Total assets	(705.5)		(705.5)
Liabilities and equity
Accounts payable, trade	20.4		20.4
Contract liabilities	(816.8)		(816.8)
Income taxes payable	18.3		18.3
Other current liabilities (Note 8)	(27.7)		(27.7)
Total current liabilities	(805.8)		(805.8)
Deferred income taxes	(8.4)		(8.4)
Commitments and contingent liabilities (Note 15)
Stockholders’ equity (Note 12)
Retained earnings	108.3		108.3
Total TechnipFMC plc stockholders’ equity	108.3		108.3
Noncontrolling interests	0.4		0.4
Total equity	108.7		108.7
Total liabilities and equity	(705.5)		(705.5)
Calculated under revenue guidance in effect before Topic 606
Revenue:
Lease and other revenue	53.3		102.7
Total revenue	3,008.0		6,097.0
Costs and expenses
Cost of service revenue	1,842.1		3,780.7
Cost of product revenue	546.2		1,078.0
Cost of lease and other revenue	31.2		68.5
Selling, general and administrative expense	281.4		584.5
Research and development expense	53.6		94.7
Impairment, restructuring and other expenses (Note 14)	11.4		22.9
Merger transaction and integration costs (Note 2)	9.0		14.6
Total costs and expenses	2,774.9		5,643.9
Other income (expense), net	2.2		(23.0)
Income from equity affiliates (Note 9)	40.2		54.2
Income before net interest expense and income taxes	275.5		484.3
Net interest expense	(50.9)		(138.3)
Income before income taxes	224.6		346.0
Provision for income taxes (Note 16)	83.1		127.2
Net income	141.5		218.8
Net (income) loss attributable to noncontrolling interests	(5.0)		(1.2)
Net income attributable to TechnipFMC plc	136.5		217.6
Assets
Cash and cash equivalents	5,555.4		5,555.4
Trade receivables, net	1,082.2		1,082.2
Contract assets	1,822.8		1,822.8
Inventories, net (Note 7)	1,110.6		1,110.6
Derivative financial instruments (Note 17)	83.9		83.9
Income taxes receivable	338.8		338.8
Advances paid to suppliers	300.0		300.0
Other current assets (Note 8)	866.4		866.4
Total current assets	11,160.1		11,160.1
Investments in equity affiliates	346.6		346.6
Property, plant and equipment, net of accumulated depreciation	3,697.8		3,697.8
Goodwill	9,009.8		9,009.8
Intangible assets, net of accumulated amortization	1,253.8		1,253.8
Deferred income taxes	418.9		418.9
Derivative financial instruments (Note 17)	84.6		84.6
Other assets	381.4		381.4
Total assets	26,353.0		26,353.0
Liabilities and equity
Less: current borrowings	78.5		78.5
Accounts payable, trade	2,945.0		2,945.0
Contract liabilities	3,156.5		3,156.5
Accrued payroll	350.7		350.7
Derivative financial instruments (Note 17)	97.9		97.9
Income taxes payable	273.6		273.6
Other current liabilities (Note 8)	1,449.7		1,449.7
Total current liabilities	8,351.9		8,351.9
Long-term debt, less current portion (Note 11)	3,787.5		3,787.5
Accrued pension and other post-retirement benefits, less current portion	242.4		242.4
Derivative financial instruments (Note 17)	88.3		88.3
Deferred income taxes	347.4		347.4
Other liabilities	379.2		379.2
Commitments and contingent liabilities (Note 15)
Redeemable noncontrolling interest	39.7		39.7
Stockholders’ equity (Note 12)
Ordinary shares	457.5		457.5
Ordinary shares held in employee benefit trust	(3.9)		(3.9)
Capital in excess of par value of ordinary shares	10,335.5		10,335.5
Retained earnings	3,484.8		3,484.8
Accumulated other comprehensive loss	(1,180.1)		(1,180.1)
Total TechnipFMC plc stockholders’ equity	13,093.8		13,093.8
Noncontrolling interests	22.8		22.8
Total equity	13,116.6		13,116.6
Total liabilities and equity	26,353.0		26,353.0
Services
Revenue:
Revenue	2,243.9	3,134.3	4,671.3	5,926.1
Services | Difference between revenue guidance in effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue:
Revenue	46.2		13.6
Services | Calculated under revenue guidance in effect before Topic 606
Revenue:
Revenue	2,290.1		4,684.9
Products
Revenue:
Revenue	663.7	$ 654.8	1,312.1	$ 1,217.3
Products | Difference between revenue guidance in effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue:
Revenue	0.9		(2.7)
Products | Calculated under revenue guidance in effect before Topic 606
Revenue:
Revenue	$ 664.6		$ 1,309.4