Goodwill and Identifiable Assets Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Goodwill [Roll Forward]
Gross goodwill, period start	$ 1,420.7	$ 1,291.3
Purchase price adjustment	3.3
Translation adjustment	(0.4)	(0.1)
Gross goodwill, period end	1,569.5	1,420.7
Commercial Business
Goodwill [Roll Forward]
Gross goodwill, period start	778.6	738.4
Purchase price adjustment	0.0
Translation adjustment	(0.4)	(0.1)
Gross goodwill, period end	829.3	778.6
Federal Government Business
Goodwill [Roll Forward]
Gross goodwill, period start	642.1	552.9
Purchase price adjustment	3.3
Translation adjustment	0.0	0.0
Gross goodwill, period end	740.2	642.1
Other Acquisitions
Goodwill [Roll Forward]
Acquisitions		129.5
Goodwill, expected tax deductible amount		77.1
Other Acquisitions \| Commercial Business
Goodwill [Roll Forward]
Acquisitions		40.3
Other Acquisitions \| Federal Government Business
Goodwill [Roll Forward]
Acquisitions		$ 89.2
2021 Acquisitions
Goodwill [Roll Forward]
Acquisitions	145.9
Goodwill, expected tax deductible amount	127.2
2021 Acquisitions \| Commercial Business
Goodwill [Roll Forward]
Acquisitions	51.1
2021 Acquisitions \| Federal Government Business
Goodwill [Roll Forward]
Acquisitions	$ 94.8

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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