v3.7.0.1
Document and Entity Information - shares
3 Months Ended
Mar. 31, 2017
Apr. 28, 2017
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Mar. 31, 2017  
Document Fiscal Year Focus 2017  
Document Fiscal Period Focus Q1  
Entity Registrant Name MRC GLOBAL INC.  
Entity Central Index Key 0001439095  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Common Stock [Member]    
Entity Common Stock, Shares Outstanding   94,473,416
Restricted Stock [Member]    
Entity Common Stock, Shares Outstanding   248,208