Postretirement Plans - Schedule of Level 3 Reconciliation (Details) - Vencore Holding Corp. and KGS Holding Corp. - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year	$ 408,018
Fair value of plan assets at end of year	427,929	$ 408,018
Hedge Funds
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year	33,878
Fair value of plan assets at end of year	30,384	33,878
Unobservable inputs
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year	80,980	47,926
Adjusted fair value of plan assets at beginning of year	76,155
Actual Return on Plan Assets	3,437	3,252
Purchases, Sales and Settlements Net	(452)	29,802
Fair value of plan assets at end of year	79,140	80,980
Unobservable inputs \| Real Estate Funds
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year	47,102	24,732
Adjusted fair value of plan assets at beginning of year	47,102
Actual Return on Plan Assets	2,106	2,370
Purchases, Sales and Settlements Net	(452)	20,000
Fair value of plan assets at end of year	48,756	47,102
Unobservable inputs \| Hedge Funds
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year	33,878	23,194
Adjusted fair value of plan assets at beginning of year	29,053
Actual Return on Plan Assets	1,331	882
Purchases, Sales and Settlements Net	0	9,802
Fair value of plan assets at end of year	$ 30,384	$ 33,878

Defined Benefit Plan, Adjusted Fair Value of Plan Assets

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

+ References

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)(iv)(02)(A)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

+ References

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

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from purchases, sales and settlements.

+ References

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)(iv)(02)(B)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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