Goodwill and Identifiable Assets (Goodwill) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Goodwill [Roll Forward]
Gross goodwill	$ 1,569.6	$ 1,569.5	$ 1,420.7
Goodwill, Purchase Accounting Adjustments	0.3	3.3
Translation adjustment	(0.2)	(0.4)
Federal Government Business
Goodwill [Roll Forward]
Gross goodwill	740.2	740.2	642.1
Goodwill, Purchase Accounting Adjustments	0.0	3.3
Translation adjustment	0.0	0.0
Commercial Business
Goodwill [Roll Forward]
Gross goodwill	829.4	829.3	$ 778.6
Goodwill, Purchase Accounting Adjustments	0.3	0.0
Translation adjustment	$ (0.2)	(0.4)
2020 Acquisitions
Goodwill [Roll Forward]
Business Acquisition, Goodwill, Expected Tax Deductible Amount		127.2
2021 Acquisitions
Goodwill [Roll Forward]
Goodwill, Acquired During Period		145.9
2021 Acquisitions \| Federal Government Business
Goodwill [Roll Forward]
Goodwill, Acquired During Period		94.8
2021 Acquisitions \| Commercial Business
Goodwill [Roll Forward]
Goodwill, Acquired During Period		$ 51.1

The amount of goodwill arising from a business combination that is expected to be deductible for tax purposes.

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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.

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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.

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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

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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

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