Business Combination - Additional Information (Detail) - USD ($) $ in Millions				3 Months Ended	6 Months Ended	9 Months Ended
	May 10, 2018		May 09, 2018	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2018	Dec. 31, 2017	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				$ 4,708		4,708
Outstanding RPOs				11,512		11,512	$ 3,901
Revenue recognized in RPOs					$ 45
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		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	4,708	[1]		4,700		4,700
Outstanding RPOs	8,300
Revenue recognized in RPOs	224
Business combination revenue recognized						2,800
Business combination operating income recognized						168
Business combination, restructuring and integration costs						61
Transaction costs				$ 5		$ 45
Initial purchase price allocation adjustments to acquired contracts	$ 341				744
Increase in goodwill due to adjustments					$ 782
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] 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 $4.7 billion of estimated goodwill recorded in conjunction with the Combination, $1.7 billion is deductible for tax purposes. Given the proximity of the Combination Date to the reporting date of September 30, 2018, the allocation of goodwill for each of our operating groups is in process, and therefore has not been presented.