Business Combination - Additional Information (Detail) - USD ($) $ in Millions			3 Months Ended		6 Months Ended
		May 10, 2018	Jun. 30, 2019		Jun. 30, 2018	Dec. 31, 2018	Dec. 18, 2017
Business Acquisition [Line Items]
Number of equity shares issued for business acquisition					85,000,000
Business combination, ownership percentage							53.00%
Business combination, net of cash acquired		$ 4,100			$ 2,374
Estimated fair value of the net tangible and identifiable intangible assets acquired recorded as goodwill			$ 2,704	[1]		$ 2,654
Outstanding RPOs			20,547			$ 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	[2]	4,990
Adjustments to assets and liabilities			$ 107
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] At June 30, 2019, we had approximately $2.2 billion of cumulative impairment charges recorded in conjunction with our impairment analysis performed during the fourth quarter of 2018, as further described in the 2018 Form 10-K.

[2] 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 approximately $5 billion of goodwill recorded in conjunction with the Combination, approximately $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.