Entity information	6 Months Ended
	Mar. 31, 2012	Apr. 15, 2012 Common stock, Class A [Member]	Apr. 15, 2012 Common stock, Class B [Member]
Entity Information [Abstract]
Current fiscal year end date	--09-30
Entity central index key	0001339947
Entity current reporting status	Yes
Entity filer category	Large Accelerated Filer
Entity registrant name	Viacom Inc.
Entity voluntary filers	No
Entity well-known seasoned issuer	Yes
Statement [Line Items]
Entity Common Stock, Shares Outstanding		51,410,792	476,409,467