With respect to a business combination completed during the period, this element provides a description of the business, other than the name, which may include the industry, size, products and other important information.

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Date when the acquirer obtains control of the acquiree, in CCYY-MM-DD format.

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Name of the acquired entity.

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Amount of assets, excluding financial assets and goodwill, that lack physical substance, having a projected indefinite period of benefit, acquired at the acquisition date.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Acquisitions Business Combinations Additional Information (Details) - USD ($) $ in Millions			3 Months Ended		12 Months Ended
	Jan. 24, 2020	Oct. 17, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Business Acquisition [Line Items]
Cash paid for acquisitions, net of cash acquired			$ 85.5	$ 48.8
Goodwill			1,547.0		$ 1,486.9
BlackStone Federal
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Jan. 24, 2020
Business Acquisition, Name of Acquired Entity	Blackstone Technology Group
Cash paid for acquisitions, net of cash acquired	$ 85.5
Business Acquisition, Description of Acquired Entity	headquartered in Arlington, Virginia
Business Combination, Reason for Business Combination	The acquisition expands the Company's capabilities in agile application development, cloud modernization and systems architecture, cybersecurity, user experience design and branding services to government clients
Goodwill, Acquired During Period	$ 61.1		$ 61.1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	$ 22.8
Intersys
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition		Oct. 17, 2019
Business Acquisition, Name of Acquired Entity		Intersys Consulting, LLC
Cash paid for acquisitions, net of cash acquired		$ 67.0
Business Acquisition, Description of Acquired Entity		headquartered in Austin, Texas
Business Combination, Reason for Business Combination		The acquisition expands the Company's capabilities in digital innovation and enterprise solutions
Goodwill		$ 41.4
Goodwill, Acquired During Period					$ 41.4
Business Acquisition, Goodwill, Expected Tax Deductible Amount		38.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets		$ 23.8
Minimum [Member] \| BlackStone Federal
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	1 year
Minimum [Member] \| Intersys
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life		3 years
Maximum [Member] \| BlackStone Federal
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	9 years
Maximum [Member] \| Intersys
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life		10 years