Document and Entity Information In Millions, unless otherwise specified	6 Months Ended
	May 31, 2012	Jun. 25, 2012
Document and Entity Information [Abstract]
Entity Registrant Name	GENCORP INC
Entity Central Index Key	0000040888
Document Type	10-Q
Document Period End Date	May 31, 2012
Amendment Flag	false
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--11-30
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		60.2