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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income attributable to McDermott	$ 2	$ 95	$ 84	$ 153
Weighted average common stock (basic)	180	95	140	90
Effect of dilutive securities:
Tangible equity units				4
Stock options, restricted stock and restricted stock units	1		1	1
Potential dilutive common stock	181	95	141	95
Net income per share attributable to McDermott
Basic:	$ 0.01	$ 1.00	$ 0.60	$ 1.70
Diluted:	$ 0.01	$ 1.00	$ 0.60	$ 1.61