Document and Entity Information (USD $)
In Millions, unless otherwise specified
9 Months Ended
Aug. 31, 2011
Sep. 23, 2011
May 31, 2010
Document and Entity Information [Abstract]      
Entity Registrant Name GENCORP INC    
Entity Central Index Key 0000040888    
Document Type 10-Q    
Document Period End Date Aug. 31, 2011    
Amendment Flag false    
Document Fiscal Year Focus 2011    
Document Fiscal Period Focus Q3    
Current Fiscal Year End Date --11-30    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Filer Category Accelerated Filer    
Entity Public Float     $ 305
Entity Common Stock, Shares Outstanding   58.7