Document and Entity Information - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Feb. 17, 2017	Jul. 05, 2015
Document and Entity Information
Entity Registrant Name	ORBITAL ATK, INC.
Entity Central Index Key	0000866121
Document Type	10-KT/A
Document Period End Date		Dec. 31, 2015
Amendment Flag	true
Amendment Description	The Restatement corrects misstatements primarily related to the estimation of contract costs on a long term contract and the Company's accounting policy which resulted in incorrect measurement of forward loss.
Current Fiscal Year End Date		--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	No
Entity Filer Category	Large Accelerated Filer
Entity Public Float				$ 4,235
Entity Common Stock, Shares Outstanding			57,546,630
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY