CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Income Statement [Abstract]
Revenues	[1]	$ 8,431,000,000		$ 6,705,000,000		$ 2,985,000,000
Costs and Expenses:
Cost of operations		8,210,000,000		6,104,000,000		2,449,000,000
Project intangibles and inventory-related amortization		34,000,000		83,000,000
Total cost of operations		8,244,000,000		6,187,000,000		2,449,000,000
Research and development expenses		36,000,000		20,000,000		5,000,000
Selling, general and administrative expenses		284,000,000		282,000,000		204,000,000
Other intangibles amortization		87,000,000		62,000,000
Transaction costs		57,000,000		48,000,000		9,000,000
Restructuring and integration costs		114,000,000		134,000,000		0
Goodwill impairment	[2]	1,430,000,000		2,168,000,000
Intangible assets impairment		162,000,000
Other asset impairments		18,000,000		58,000,000		1,000,000
Loss (gain) on asset disposals		104,000,000		3,000,000		(2,000,000)
Total expenses		10,536,000,000		8,962,000,000		2,666,000,000
Income (loss) from investments in unconsolidated affiliates		34,000,000		13,000,000		(12,000,000)
Investment in unconsolidated affiliates-related amortization		(11,000,000)		(12,000,000)
Operating (loss) income		(2,082,000,000)		(2,256,000,000)		307,000,000
Other expense:
Interest expense, net		(735,000,000)		(259,000,000)		(63,000,000)
Other non-operating income (expense), net		(9,000,000)		(56,000,000)		5,000,000
Total other expense, net		(744,000,000)		(315,000,000)		(58,000,000)
(Loss) income before provision for income taxes		(2,826,000,000)		(2,571,000,000)		249,000,000
Income tax expense		58,000,000		104,000,000		69,000,000
Non-operating loss from investments in unconsolidated affiliates				(3,000,000)		(2,000,000)
Net (loss) income		(2,884,000,000)		(2,678,000,000)		178,000,000
Less: Net income (loss) attributable to noncontrolling interests		25,000,000		9,000,000		(1,000,000)
Net (loss) income attributable to McDermott		(2,909,000,000)	[3]	(2,687,000,000)	[3]	179,000,000	[4]
Dividends on redeemable preferred stock	[3]	(44,000,000)		(3,000,000)
Accretion of redeemable preferred stock	[3]	(16,000,000)		(1,000,000)
Net (loss) income attributable to common stockholders		$ (2,969,000,000)	[3]	$ (2,691,000,000)	[3]	$ 179,000,000	[4]
Net (loss) income per share attributable to common stockholders
Basic		$ (16.31)	[3]	$ (17.94)	[3]	$ 1.97	[4]
Diluted		$ (16.31)	[3]	$ (17.94)	[3]	$ 1.88	[4]
Shares used in the computation of net (loss) income per share
Basic		182	[3]	150	[3]	91	[4]
Diluted		182	[3]	150	[3]	95	[4]

[1] Intercompany amounts have been eliminated in consolidation.

[2] Represents impairment of goodwill associated with our NCSA and EARC reporting units in 2019 and our NCSA, EARC, APAC and Technology reporting units in 2018. See Note 9, Goodwill and Other Intangible Assets, for further discussion. The goodwill impairment values are included within the applicable operating group’s Operating loss.

[3] ^{The effects of restricted stock, warrants and redeemable preferred stock were not included in the calculation of diluted earnings per share for 2019 and 2018 due to the net losses for each such year.}

[4] ^{Approximately 0.5 million shares of underlying outstanding stock-based awards in 2017 were excluded from the computation of diluted earnings per share during such year because the exercise price of those awards was greater than the average market price of our common stock, and the inclusion of such shares would have been antidilutive during such year.}