Document and Entity Information
3 Months Ended
Mar. 31, 2013
Apr. 26, 2013
Document Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Mar. 31, 2013  
Document Fiscal Year Focus 2013  
Document Fiscal Period Focus Q1  
Trading Symbol MRC  
Entity Registrant Name MRC GLOBAL INC.  
Entity Central Index Key 0001439095  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Common Stock, Shares Outstanding   101,687,820