CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (2,884)	$ (2,678)	$ 178
Other comprehensive (loss) income, net of tax:
(Loss) gain on derivatives	28	(38)	23
Actuarial pension gains		6
Foreign currency translation	(24)	(24)	(7)
Total comprehensive (loss) income	(2,880)	(2,734)	194
Less: Comprehensive income (loss) attributable to noncontrolling interests	25	9	(1)
Comprehensive (loss) income attributable to McDermott	$ (2,905)	$ (2,743)	$ 195