Business Combination - Additional Information (Detail) - USD ($) $ in Millions			12 Months Ended
		May 10, 2018	Dec. 31, 2019	Dec. 31, 2018		Dec. 18, 2017
Business Acquisition [Line Items]
Number of equity shares issued for business acquisition	[1]			85,000,000
Business combination, ownership percentage						53.00%
Business combination, net of cash acquired		$ 4,100	$ 7	$ 2,374
Estimated fair value of the net tangible and identifiable intangible assets acquired recorded as goodwill			1,286	2,654	[2]
Outstanding RPOs			$ 18,638	$ 10,913
Chicago Bridge & Iron Company N.V. [Member]
Business Acquisition [Line Items]
Business acquisition, date of acquisition agreement		Dec. 18, 2017
Business acquisition, combination date		May 10, 2018
Business combination, consideration		$ 2,870
Number of equity shares issued for business acquisition		84,500,000
Business combination, number of McDermott's shares entitled for each share of CB&I owned		85
Business combination, number of converted shares acquired		2,200,000
Business combination, gross purchase price		$ 4,565
Business combination, net of cash acquired		4,067
Estimated fair value of the net tangible and identifiable intangible assets acquired recorded as goodwill	[3]	4,990
Outstanding RPOs		$ 8,300
Chicago Bridge & Iron Company N.V. [Member] | Effect of Reverse Stock Split [Member]
Business Acquisition [Line Items]
Business combination, number of McDermott's shares entitled for each share of CB&I owned		0.82407

[1] As discussed in Note 3, Business Combination, in May 2018, we issued 84.5 million shares of McDermott common stock to the former CB&I shareholders. Additionally, effective as of the Combination Date, unvested and unexercised stock-settled equity-based awards (which included 2.1 million of CB&I restricted stock units and stock options to purchase 0.1 million shares of CB&I’s common stock) were canceled and converted into comparable McDermott stock-settled awards with generally the same terms and conditions as those prior to the Combination Date. The restricted stock units generally vest over a period ranging from three to four years from the original grant date.

[2] As of December 31, 2018, we had approximately $2.2 billion of cumulative impairment charges recorded in conjunction with our impairment assessment performed during the fourth quarter of 2018, as previously described in the 2018 Form 10-K.

[3] Goodwill resulted from the acquired established workforce, which does not qualify for separate recognition, as well as expected future cost savings and revenue synergies associated with the combined operations. Of the $5 billion of goodwill recorded in conjunction with the Combination, $2.7 billion, $461 million, $50 million, $52 million and $1.7 billion was allocated to our NCSA, EARC, MENA, APAC and Technology reporting segments, respectively. Approximately $1.7 billion of the opening goodwill balance is deductible for tax purposes. See Note 9, Goodwill and Other Intangible Assets, for our discussion of impairment charges recorded during 2019 and our changes in estimates.