Quarterly Financial Data (Unaudited) - Selected Unaudited Quarterly Financial Information (Detail) - USD ($)	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018	[1]	Sep. 30, 2018	[1]	Jun. 30, 2018	[1]	Mar. 31, 2018	[1]	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 1,962,000,000		$ 2,121,000,000		$ 2,137,000,000		$ 2,211,000,000		$ 2,073,000,000		$ 2,289,000,000		$ 1,735,000,000		$ 608,000,000		$ 8,431,000,000		$ 6,705,000,000		$ 2,985,000,000
Project intangibles and inventory related amortization	7,000,000	[2]	7,000,000	[2]	10,000,000	[2]	10,000,000	[2]	41,000,000	[2]	30,000,000	[2]	12,000,000	[2]			34,000,000		83,000,000
Gross profit	(115,000,000)		(59,000,000)		178,000,000		183,000,000		(122,000,000)		273,000,000		237,000,000		130,000,000
Other intangibles amortization	22,000,000	[3]	21,000,000	[3]	22,000,000	[3]	22,000,000	[3]	27,000,000	[3]	25,000,000	[3]	10,000,000	[3]			87,000,000		62,000,000
Transaction costs	28,000,000	[4]	14,000,000	[4]	11,000,000	[4]	4,000,000	[4]	3,000,000	[5]	5,000,000	[5]	37,000,000	[5]	3,000,000	[5]	57,000,000		48,000,000		9,000,000
Restructuring and integration costs	11,000,000	[6]	14,000,000	[6]	20,000,000	[6]	69,000,000	[6]	28,000,000	[6]	31,000,000	[6]	63,000,000	[6]	12,000,000	[6]	114,000,000		134,000,000		0
Goodwill impairment	60,000,000	[7]	1,370,000,000	[7]					2,168,000,000	[8]							1,430,000,000	[9]	2,168,000,000	[9]
Intangible Asset impairments	19,000,000	[10]	143,000,000	[10]													162,000,000
Other asset impairments			18,000,000	[11]					58,000,000	[11]							18,000,000		58,000,000		1,000,000
Loss on asset disposals	2,000,000				102,000,000												(104,000,000)		(3,000,000)		2,000,000
Net income (loss)	(849,000,000)	[12]	(1,864,000,000)	[12]	(114,000,000)	[12]	(57,000,000)	[12]	(2,757,000,000)				45,000,000		34,000,000		(2,884,000,000)		(2,678,000,000)		178,000,000
Net (loss) income attributable to McDermott	(848,000,000)		(1,873,000,000)		(132,000,000)		(56,000,000)		(2,771,000,000)		2,000,000		47,000,000		35,000,000		(2,909,000,000)	[13]	(2,687,000,000)	[13]	179,000,000	[14]
Dividends on redeemable preferred stock	(14,000,000)	[15]	(10,000,000)	[15]	(10,000,000)	[15]	(10,000,000)	[15]	(3,000,000)	[15]							(44,000,000)	[13]	(3,000,000)	[13]
Accretion of redeemable preferred stock	(4,000,000)	[15]	(4,000,000)	[15]	(4,000,000)	[15]	(4,000,000)	[15]	(1,000,000)	[15]							(16,000,000)	[13]	(1,000,000)	[13]
Net income (loss) attributable to common stockholders	$ (866,000,000)		$ (1,887,000,000)		$ (146,000,000)		$ (70,000,000)		$ (2,775,000,000)		$ 2,000,000		$ 47,000,000		$ 35,000,000		$ (2,969,000,000)	[13]	$ (2,691,000,000)	[13]	$ 179,000,000	[14]
Income (loss) per share
Basic	$ (4.69)		$ (10.37)		$ (0.80)		$ (0.39)		$ (15.33)		$ 0.01		$ 0.33		$ 0.12		$ (16.31)	[13]	$ (17.94)	[13]	$ 1.97	[14]
Diluted	$ (4.69)		$ (10.37)		$ (0.80)		$ (0.39)		$ (15.33)		$ 0.01		$ 0.33		$ 0.12		$ (16.31)	[13]	$ (17.94)	[13]	$ 1.88	[14]

[1] Results in the second, third and fourth quarters of 2018 reflect impacts of the Combination from the Combination Date.

[2] Represents amortization of fair value adjustments for RPOs acquired in the Combination and normalized profit margin fair value associated with acquired long-term contracts that were deemed to be lower than market value as of the Combination Date. Also included is amortization associated with fair value adjustments to inventory balances acquired in the Combination.

[3] Represents amortization of other intangible assets acquired in the Combination. See Note 9, Goodwill and Other Intangible Assets, for further discussion.

[4] 2019—primarily relates to legal and other professional fees associated with the sale processes for the pipe fabrication business and the Lummus Technology business and the now-terminated effort to sell our industrial storage tanks business, as well as professional and other fees associated with the Chapter 11 Cases.

[5] 2018—primarily relates to professional service fees (including audit, legal and advisory services) associated with the Combination. See Note 3, Business Combination, for further discussion.

[6] Primarily represents costs related to achieve our CPI. See Note 12, Restructuring and Integration Costs, for further discussion.

[7] 2019—represents impairment of goodwill associated with our NCSA and EARC reporting units, resulting from our interim and annual impairment assessment. See Note 9, Goodwill and Other Intangible Assets, for further discussion.

[8] 2018—represents impairment of goodwill associated with our NCSA, EARC, APAC and Technology reporting units, resulting from our annual impairment assessment.

[9] 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.

[10] Represents impairment of intangible assets, primarily in our NCSA segment. See Note 9, Goodwill and Other Intangible Assets, for further discussion.

[11] Represents charges associated with the impairment of vessels and other marine equipment, due to changes in their level of planned utilization. See Note 16, Fair Value Measurements, for further discussion.

[12] Net loss for the quarter ended December 31, 2019 included the impact on interest expense of: (1) $316 million of DIC amortization, primarily associated with the accelerated DIC amortization due to our non-compliance with certain covenants and other obligations contained in our financing arrangements, discussed in Note 13, Debt; (2) $67 million of expense associated with our interest rate swap arrangement, reclassified from AOCI into interest expense, discussed in Note 17, Derivative Financial Instruments; and (3) a $32 million of gain associated with the valuation of the Superpriority Credit Agreement embedded derivative, discussed in Note 13, Debt.

[13] ^{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.}

[14] ^{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.}

[15] Represents dividends paid and accrued on the shares of 12% Redeemable Preferred Stock and accretion of the stock over the seven years from November 29, 2018 through the expected redemption date of November 29, 2025, using the effective interest method.  See Note 21, Redeemable Preferred Stock, for further discussion