Quarterly Financial Data (Unaudited) - Selected Unaudited Quarterly Financial Information (Detail) - USD ($)	3 Months Ended																12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017	[2]	Sep. 30, 2017	[3]	Jun. 30, 2017	[4]	Mar. 31, 2017	[5]	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 2,073,000,000	[1]	$ 2,289,000,000	[1]	$ 1,735,000,000	[1]	$ 608,000,000	[1]	$ 718,000,000		$ 959,000,000		$ 789,000,000		$ 519,000,000		$ 6,705,000,000		$ 2,985,000,000		$ 2,636,000,000
Project intangibles and inventory related amortization	41,000,000	[6]	30,000,000	[6]	12,000,000	[6]											83,000,000
Gross profit	(122,000,000)	[1]	273,000,000	[1]	237,000,000	[1]	130,000,000	[1]	122,000,000		185,000,000		139,000,000		90,000,000
Other intangibles amortization	27,000,000	[7]	25,000,000	[7]	10,000,000	[7]											62,000,000
Transaction costs	3,000,000	[8]	5,000,000	[8]	37,000,000	[8]	3,000,000	[8]									48,000,000		9,000,000
Restructuring and integration costs	28,000,000	[9]	31,000,000	[9]	63,000,000	[9]	12,000,000	[9]									134,000,000		0		11,000,000
Goodwill impairment	2,168,000,000	[10]															2,168,000,000	[11]
Other asset impairments	58,000,000	[12]															58,000,000		1,000,000		55,000,000
Net income (loss)	(2,757,000,000)				45,000,000		34,000,000		24,000,000		94,000,000		36,000,000		24,000,000		(2,678,000,000)		178,000,000		36,000,000
Net (loss) income attributable to McDermott	(2,771,000,000)		2,000,000		47,000,000		35,000,000		$ 26,000,000		$ 95,000,000		$ 36,000,000		$ 22,000,000		(2,687,000,000)	[13]	179,000,000	[14]	34,000,000	[14]
Dividends on redeemable preferred stock	(3,000,000)	[15]															(3,000,000)	[13]
Accretion of redeemable preferred stock	(1,000,000)	[15]															(1,000,000)	[13]
Net income (loss) attributable to common stockholders	$ (2,775,000,000)		$ 2,000,000		$ 47,000,000		$ 35,000,000										$ (2,691,000,000)	[13]	$ 179,000,000	[14]	$ 34,000,000	[14]
Income (loss) per share
Basic	$ (15.33)		$ 0.01		$ 0.33		$ 0.12		$ 0.28		$ 1.00		$ 0.38		$ 0.27		$ (17.94)	[13]	$ 1.97	[14]	$ 0.43	[14]
Diluted	$ (15.33)		$ 0.01		$ 0.33		$ 0.12		$ 0.27		$ 1.00		$ 0.38		$ 0.23		$ (17.94)	[13]	$ 1.88	[14]	$ 0.36	[14]

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

[2] Operating results for the fourth quarter of 2017 were primarily driven by higher fabrication and marine activity in the MENA segment and installation progress on the Inpex Ichthys project.

[3] Operating results for the third quarter of 2017 reflect high quality operational performance, while operating with peak levels of utilization in the MENA segment and progressing on the Inpex Ichthys project.

[4] Operating results for the second quarter of 2017 continued to reflect efficient project execution and higher engineering, fabrication and marine activity and improved productivity on multiple projects primarily in our MENA segment.

[5] The first quarter of 2017 operating results improvement was driven by strong cost management, with significantly lower project costs in our MENA and APAC segments, and improvements in our selling, general and administrative expenses.

[6] 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.

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

[8] Transaction costs relate to professional service fees (including audit, legal and advisory services) associated with the Combination. See Note 3, Business Combination, for further discussion.

[9] Restructuring and integration costs primarily relate to costs to achieve our CPI. See Note 12, Restructuring and Integration Costs, for further discussion.

[10] Represents impairment of goodwill associated with our NCSA, EARC, APAC and Technology reporting units, resulting from our annual impairment assessment. See Note 9, Goodwill and Other Intangible Assets, for further discussion.

[11] Represents impairment of goodwill associated with our NCSA, EARC, APAC and Technology reporting units, resulting from our impairment assessment during the fourth quarter of 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.

[12] Represents charges associated with the impairment of two vessels within our Corporate operating group, due to changes in their level of planned utilization during 2018. See Note 16, Fair Value Measurements, for further discussion.

[13] The effects of restricted stock, warrants and redeemable preferred stock were not included in the calculation of diluted earnings per share for 2018 due to the net loss for the period.

[14] Approximately 0.5 million and 0.7 million shares underlying outstanding stock-based awards in 2017 and 2016 were excluded from the computation of diluted earnings per share during those periods 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 in each of those years.

[15] Represents dividends paid 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.