Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2019		Sep. 30, 2018
Earnings Per Share [Abstract]
Net (loss) income attributable to McDermott		$ (1,873)	[1]	$ 2	[2]	$ (2,061)	[1]	$ 84	[2]
Dividends on redeemable preferred stock	[1]	(10)				(30)
Accretion of redeemable preferred stock	[1]	(4)				(12)
Net (loss) income attributable to common stockholders		$ (1,887)	[1]	$ 2	[2]	$ (2,103)	[1]	$ 84	[2]
Weighted average common stock (basic)		182	[1]	180	[2]	181	[1]	140	[2]
Effect of dilutive securities:
Stock-based awards	[2]			1				1
Weighted average common stock (diluted)		182	[1]	181	[2]	181	[1]	141	[2]
Net (loss) income per share attributable to common stockholders
Basic:		$ (10.37)	[1]	$ 0.01	[2]	$ (11.62)	[1]	$ 0.60	[2]
Diluted:		$ (10.37)	[1]	$ 0.01	[2]	$ (11.62)	[1]	$ 0.60	[2]

[1] ^{The effects of stock-based awards, warrants and redeemable preferred stock were not included in the calculation of diluted earnings per share for the three and nine months ended September 30, 2019 due to the net loss for the periods.}

[2] ^{Approximately 0.5 million shares underlying outstanding stock-based awards for the three and nine months ended September 30, 2018 were excluded from the computation of diluted earnings per share during the 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 periods.}