Postretirement Plans - Benefit Obligations and Funded Status (Narrative) (Details) - Vencore Holding Corp. and KGS Holding Corp. - Pension Plan - USD ($) $ in Thousands		12 Months Ended
Dec. 01, 2016	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Actuarial gains and losses included in accumulated other comprehensive income		$ 4,800
Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Lump sum payment	$ 18,800	$ 0	$ 18,845

Amount of payment, which decreases plan assets of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(ii)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(iv)(01)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(8)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Balance Type:	credit
Period Type:	duration