CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (1,864)		$ (2,035)	$ 79
Other comprehensive (loss) income, net of tax:
Loss on derivatives	(28)	$ (1)	(68)	(13)
Foreign currency translation	(13)	(8)	(47)	(20)
Total comprehensive (loss) income	(1,905)	(9)	(2,150)	46
Less: Comprehensive income (loss) attributable to noncontrolling interests	9	(2)	26	(5)
Comprehensive (loss) income attributable to McDermott	$ (1,914)	$ (7)	$ (2,176)	$ 51