Reorganization - Schedule of Condensed Consolidated Statements of Operations (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Reorganization [Line Items]
Revenues	$ 1,906	$ 2,063
Costs and Expenses:
Cost of operations	1,853	1,928
Total expenses	2,955	2,087
Operating loss	(1,051)	(25)
Other expense:
Interest expense, net	(56)	(92)
Reorganization items, net	(246)
Other non-operating income, net	3	1
Total other expense, net	(299)	(91)
Loss from continuing operations before provision for income taxes	(1,350)	(116)
Income tax expense (benefit)	8	(21)
Net loss from continuing operations	(1,358)	(95)
Net (loss) income from discontinued operations	(14)	38
Net loss	(1,372)	(57)
Less: Net income (loss) attributable to noncontrolling interests	6	(1)
Net loss attributable to McDermott	(1,378)	$ (56)
Debtor in Possession [Member]
Reorganization [Line Items]
Revenues	1,757
Costs and Expenses:
Cost of operations	1,732
Other operating expenses, net	1,087
Total expenses	2,819
Operating loss	(1,062)
Other expense:
Interest expense, net	(58)
Intercompany charges for interest	5
Reorganization items, net	(246)
Other non-operating income, net	(6)
Total other expense, net	(305)
Loss from continuing operations before provision for income taxes	(1,367)
Income tax expense (benefit)	6
Net loss from continuing operations	(1,373)
Net (loss) income from discontinued operations	(14)
Net loss	(1,387)
Less: Net income (loss) attributable to noncontrolling interests	6
Net loss attributable to McDermott	$ (1,393)