Revenue - Impact on Primary Financial Statements (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Revenue:
Lease and other revenue	$ 60.7	$ 55.1	$ 163.4	$ 144.7
Total revenue	3,143.8	4,140.9	9,229.9	11,373.9
Costs and expenses
Cost of lease and other revenue	30.9	37.5	99.4	100.2
Selling, general and administrative expense	250.6	284.4	835.1	806.5
Research and development expense	38.6	51.1	133.3	143.6
Impairment, restructuring and other expenses (Note 14)	9.7	59.4	32.6	56.8
Merger transaction and integration costs (Note 2)	6.3	9.2	20.9	87.2
Total costs and expenses	2,863.7	3,872.3	8,527.2	10,704.6
Other income (expense), net	10.4	30.0	(12.6)	43.2
Income from equity affiliates (Note 9)	16.4	17.3	70.6	39.4
Income before net interest expense and income taxes	306.9	315.9	760.7	751.9
Net interest expense	(106.0)	(86.3)	(244.3)	(240.5)
Income before income taxes	200.9	229.6	516.4	511.4
Provision for income taxes (Note 16)	66.7	111.7	180.7	249.7
Net income	134.2	117.9	335.7	261.7
Net (income) loss attributable to noncontrolling interests	2.7	3.1	2.0	5.5
Net income attributable to TechnipFMC plc	136.9	121.0	337.7	267.2
Assets
Cash and cash equivalents	5,553.3	6,896.1	5,553.3	6,896.1	$ 6,737.4	$ 6,269.3
Trade receivables, net	2,079.3		2,079.3		1,484.4
Contract assets	1,286.9		1,286.9		1,755.5
Inventories, net (Note 7)	1,171.0		1,171.0		987.0
Derivative financial instruments (Note 17)	97.0		97.0		78.3
Income taxes receivable	333.3		333.3		337.0
Advances paid to suppliers	211.5		211.5		391.3
Other current assets (Note 8)	830.9		830.9		1,206.2
Total current assets	11,563.2		11,563.2		12,977.1
Investments in equity affiliates	360.3		360.3		272.5
Property, plant and equipment, net of accumulated depreciation	3,670.5		3,670.5		3,871.5
Goodwill	9,003.4		9,003.4		8,929.8
Intangible assets, net of accumulated amortization	1,223.1		1,223.1		1,333.8
Deferred income taxes	426.8		426.8		454.7
Derivative financial instruments (Note 17)	80.0		80.0		94.9
Other assets	332.7		332.7		329.4
Total assets	26,660.0		26,660.0		28,263.7
Liabilities and equity
Less: current borrowings	78.4		78.4		77.1
Accounts payable, trade	2,800.9		2,800.9		3,958.7
Contract liabilities	3,711.9		3,711.9		3,314.2
Accrued payroll	375.5		375.5		402.2
Derivative financial instruments (Note 17)	92.1		92.1		69.0
Income taxes payable	208.2		208.2		320.3
Other current liabilities (Note 8)	1,435.8		1,435.8		1,687.9
Total current liabilities	8,702.8		8,702.8		9,829.4
Long-term debt, less current portion (Note 11)	4,017.1		4,017.1		3,777.9
Accrued pension and other post-retirement benefits, less current portion	230.1		230.1		282.0
Derivative financial instruments (Note 17)	81.2		81.2		68.1
Deferred income taxes	351.8		351.8		419.7
Other liabilities	413.0		413.0		477.2
Total liabilities	13,796.0		13,796.0		14,854.3
Commitments and contingent liabilities (Note 15)
Redeemable noncontrolling interest	39.7		39.7		0.0
Stockholders’ equity (Note 12)
Ordinary shares	452.9		452.9		465.1
Ordinary shares held in employee benefit trust	(2.4)		(2.4)		(4.8)
Capital in excess of par value of ordinary shares	10,247.1		10,247.1		10,483.3
Retained earnings	3,421.1		3,421.1		3,448.0
Accumulated other comprehensive loss	(1,313.9)		(1,313.9)		(1,003.7)
Total TechnipFMC plc stockholders’ equity	12,804.8		12,804.8		13,387.9
Noncontrolling interests	19.5		19.5		21.5
Total equity	12,824.3		12,824.3		13,409.4
Total liabilities and equity	26,660.0		26,660.0		$ 28,263.7
Difference between revenue guidance in effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue:
Total revenue	6.0		16.9
Costs and expenses
Total costs and expenses	(1.1)		(20.7)
Income before net interest expense and income taxes	7.1		37.6
Income before income taxes	7.1		37.6
Provision for income taxes (Note 16)	(18.5)		(5.3)
Net income	25.6		42.9
Net (income) loss attributable to noncontrolling interests	0.1		(0.4)
Net income attributable to TechnipFMC plc	25.7		42.5
Assets
Trade receivables, net	(1,153.2)		(1,153.2)
Contract assets	519.5		519.5
Inventories, net (Note 7)	23.4		23.4
Total current assets	(610.3)		(610.3)
Deferred income taxes	(13.9)		(13.9)
Other assets	0.8		0.8
Total assets	(623.4)		(623.4)
Liabilities and equity
Accounts payable, trade	31.5		31.5
Contract liabilities	(757.3)		(757.3)
Income taxes payable	4.9		4.9
Other current liabilities (Note 8)	(32.8)		(32.8)
Total current liabilities	(753.7)		(753.7)
Deferred income taxes	(4.0)		(4.0)
Total liabilities	(757.7)		(757.7)
Commitments and contingent liabilities (Note 15)
Stockholders’ equity (Note 12)
Retained earnings	134.0		134.0
Total TechnipFMC plc stockholders’ equity	134.0		134.0
Noncontrolling interests	0.3		0.3
Total equity	134.3		134.3
Total liabilities and equity	(623.4)		(623.4)
Calculated under revenue guidance in effect before Topic 606
Revenue:
Lease and other revenue	60.7		163.4
Total revenue	3,149.8		9,246.8
Costs and expenses
Cost of lease and other revenue	30.9		99.4
Selling, general and administrative expense	250.6		835.1
Research and development expense	38.6		133.3
Impairment, restructuring and other expenses (Note 14)	9.7		32.6
Merger transaction and integration costs (Note 2)	6.3		20.9
Total costs and expenses	2,862.6		8,506.5
Other income (expense), net	10.4		(12.6)
Income from equity affiliates (Note 9)	16.4		70.6
Income before net interest expense and income taxes	314.0		798.3
Net interest expense	(106.0)		(244.3)
Income before income taxes	208.0		554.0
Provision for income taxes (Note 16)	48.2		175.4
Net income	159.8		378.6
Net (income) loss attributable to noncontrolling interests	2.8		1.6
Net income attributable to TechnipFMC plc	162.6		380.2
Assets
Cash and cash equivalents	5,553.3		5,553.3
Trade receivables, net	926.1		926.1
Contract assets	1,806.4		1,806.4
Inventories, net (Note 7)	1,194.4		1,194.4
Derivative financial instruments (Note 17)	97.0		97.0
Income taxes receivable	333.3		333.3
Advances paid to suppliers	211.5		211.5
Other current assets (Note 8)	830.9		830.9
Total current assets	10,952.9		10,952.9
Investments in equity affiliates	360.3		360.3
Property, plant and equipment, net of accumulated depreciation	3,670.5		3,670.5
Goodwill	9,003.4		9,003.4
Intangible assets, net of accumulated amortization	1,223.1		1,223.1
Deferred income taxes	412.9		412.9
Derivative financial instruments (Note 17)	80.0		80.0
Other assets	333.5		333.5
Total assets	26,036.6		26,036.6
Liabilities and equity
Less: current borrowings	78.4		78.4
Accounts payable, trade	2,832.4		2,832.4
Contract liabilities	2,954.6		2,954.6
Accrued payroll	375.5		375.5
Derivative financial instruments (Note 17)	92.1		92.1
Income taxes payable	213.1		213.1
Other current liabilities (Note 8)	1,403.0		1,403.0
Total current liabilities	7,949.1		7,949.1
Long-term debt, less current portion (Note 11)	4,017.1		4,017.1
Accrued pension and other post-retirement benefits, less current portion	230.1		230.1
Derivative financial instruments (Note 17)	81.2		81.2
Deferred income taxes	347.8		347.8
Other liabilities	413.0		413.0
Total liabilities	13,038.3		13,038.3
Commitments and contingent liabilities (Note 15)
Redeemable noncontrolling interest	39.7		39.7
Stockholders’ equity (Note 12)
Ordinary shares	452.9		452.9
Ordinary shares held in employee benefit trust	(2.4)		(2.4)
Capital in excess of par value of ordinary shares	10,247.1		10,247.1
Retained earnings	3,555.1		3,555.1
Accumulated other comprehensive loss	(1,313.9)		(1,313.9)
Total TechnipFMC plc stockholders’ equity	12,938.8		12,938.8
Noncontrolling interests	19.8		19.8
Total equity	12,958.6		12,958.6
Total liabilities and equity	26,036.6		26,036.6
Services
Revenue:
Revenue	2,487.9	3,374.9	7,159.2	9,301.0
Costs and expenses
Cost of goods and services sold	2,046.6	2,841.3	5,846.0	7,728.4
Services | Difference between revenue guidance in effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue:
Revenue	5.4		19.0
Costs and expenses
Cost of goods and services sold	(2.4)		(21.1)
Services | Calculated under revenue guidance in effect before Topic 606
Revenue:
Revenue	2,493.3		7,178.2
Costs and expenses
Cost of goods and services sold	2,044.2		5,824.9
Products
Revenue:
Revenue	595.2	710.9	1,907.3	1,928.2
Costs and expenses
Cost of goods and services sold	481.0	$ 589.4	1,559.9	$ 1,781.9
Products | Difference between revenue guidance in effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue:
Revenue	0.6		(2.1)
Costs and expenses
Cost of goods and services sold	1.3		0.4
Products | Calculated under revenue guidance in effect before Topic 606
Revenue:
Revenue	595.8		1,905.2
Costs and expenses
Cost of goods and services sold	$ 482.3		$ 1,560.3