Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Jul. 25, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Trading Symbol	MDR
Entity Registrant Name	MCDERMOTT INTERNATIONAL INC
Entity Central Index Key	0000708819
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity File Number	001-08430
Entity Tax Identification Number	720593134
Entity Address, Address Line One	757 N. Eldridge Parkway
Entity Address, City or Town	HOUSTON
Entity Address, State or Province	TEXAS
Entity Address, Postal Zip Code	77079
City Area Code	(281)
Local Phone Number	870-5000
Entity Common Stock, Shares Outstanding		181,729,320