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Goodwill and Identifiable Assets (Goodwill) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Jan. 24, 2020	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Gross goodwill		$ 1,547.0	$ 1,486.9	$ 1,421.1
Translation adjustment		(1.0)	(0.3)
Apex
Goodwill [Roll Forward]
Gross goodwill		703.2	703.5	662.1
Translation adjustment		(0.3)
Oxford
Goodwill [Roll Forward]
Gross goodwill		229.8	230.5	230.8
Translation adjustment		(0.7)	(0.3)
ECS
Goodwill [Roll Forward]
Gross goodwill		614.0	552.9	$ 528.2
DHA
Goodwill [Roll Forward]
Goodwill, Acquired During Period			24.7
Intersys
Goodwill [Roll Forward]
Goodwill, Acquired During Period			$ 41.4
BlackStone Federal
Goodwill [Roll Forward]
Goodwill, Acquired During Period	$ 61.1	$ 61.1

X

- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

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- Definition

Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

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- Definition

Amount before accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

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- Definition

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