Business Combination - Summary of Pro Forma Financial Information (Detail) - Chicago Bridge & Iron Company N.V. [Member] - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2018	[1]	Sep. 30, 2017	Sep. 30, 2018	[1]	Sep. 30, 2017
Business Acquisition [Line Items]
Pro forma revenue		$ 2,289		$ 2,866	$ 7,135		$ 7,390
Pro forma net income (loss) attributable to McDermott		$ 33		$ 67	$ 128		$ (270)
Pro forma net income (loss) per share attributable to McDermott:
Basic		$ 0.18		$ 0.37	$ 0.71		$ (1.50)
Diluted		$ 0.18		$ 0.37	$ 0.71		$ (1.50)
Basic	[2]	180		180	180		180
Diluted		181		181	181		180

[1] Adjustments, net of tax, included in the pro forma net income above that were of a non-recurring nature totaled $28 million and $136 million for the three and nine months ended September 30, 2018, respectively. The adjustments reflect the elimination of restructuring and integration costs ($24 million and $90 million) and transaction costs ($4 million and $35 million) for the three and nine months ended September 30, 2018, respectively, and debt extinguishment costs of $11 million incurred in the first half of 2018, that were included in McDermott and CB&I’s historical results for the three and nine months ended September 30, 2018, respectively. For the comparative three and nine months ended September 30, 2017, adjustments, net of tax, included in the pro forma net income (loss) above that were of a non-recurring nature totaled $17 million and $20 million, respectively, and reflect the elimination of restructuring costs that were included in CB&I’s historical results. These pro forma results exclude the effect of adjustments to the opening balance sheet associated with fair value purchase accounting estimates.

[2] Pro forma net income (loss) per share was calculated using weighted average basic and diluted shares outstanding during the three months ended September 30, 2018. The effects of dilutive securities were not included in the calculation of diluted EPS for the nine months ended September 30, 2017 due to the net loss for that period.