Stockholder's Equity - Changes in the Number of Shares Outstanding and Treasury Shares Held by the Company (Details) - shares shares in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Shares Outstanding [Abstract]
Beginning balance		181	95
Common stock issued	[1]	13	2
Shares issued in the Combination (Note 3, Business Combination)	[2]		85
Purchase of common stock		(1)	(1)
Ending balance		193	181
Shares Held as Treasury Shares [Abstract]
Beginning balance		3	3
Purchase of common stock		1	1
Retirement of common stock		(1)	(1)
Ending balance		3	3
Common stock, shares issued		196	183

[1] In December 2019, in connection with the Superpriority Credit Agreement, discussed in Note 13, Debt, we issued approximately 11 million shares of McDermott common stock, 0.09 million of Series B Warrants (that will entitle each holder to purchase one share of common stock of McDermott, par value $1.00 per share, at a purchase price of $0.01 per share) (the “Series B Warrants” and, together with the Series A Warrants, the “Warrants”) and 0.56 million shares of Series A Preferred Stock with par value of 0.001 per share, to certain Superpriority Credit Agreement lenders.

[2] As discussed in Note 3, Business Combination, in May 2018, we issued 84.5 million shares of McDermott common stock to the former CB&I shareholders. Additionally, effective as of the Combination Date, unvested and unexercised stock-settled equity-based awards (which included 2.1 million of CB&I restricted stock units and stock options to purchase 0.1 million shares of CB&I’s common stock) were canceled and converted into comparable McDermott stock-settled awards with generally the same terms and conditions as those prior to the Combination Date. The restricted stock units generally vest over a period ranging from three to four years from the original grant date.