Document and Entity Information - shares
6 Months Ended
Jun. 30, 2019
Jul. 26, 2019
Entity File Number 001-35479  
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 MRC  
Title of 12(b) Security Common Stock, par value $0.01  
Security Exchange Name NYSE  
Entity Registrant Name MRC GLOBAL INC.  
Entity Central Index Key 0001439095  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Filer Category Large Accelerated Filer  
Entity Shell Company false  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Address, Address Line One Fulbright Tower  
Entity Address, Address Line Two 1301 McKinney Street, Suite 2300  
Entity Address, City or Town Houston  
Entity Address, State or Province TX  
Entity Address, Postal Zip Code 77010  
Entity Incorporation, State or Country Code DE  
City Area Code 877  
Local Phone Number 294-7574  
Entity Tax Identification Number 20-5956993  
Document Quarterly Report true  
Document Transition Report false  
Entity Interactive Data Current Yes  
Common Stock [Member]    
Entity Common Stock, Shares Outstanding   83,140,580
Restricted Stock [Member]    
Entity Common Stock, Shares Outstanding   74,055