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Goodwill and Identifiable Assets (Goodwill) (Details) - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Jun. 30, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Goodwill [Roll Forward] |  |  |
Gross goodwill | $ 1,475.5 | $ 1,420.7 | $ 1,291.3
Goodwill, Purchase Accounting Adjustments | 3.5 |  |
Translation adjustment |  | (0.1) |
Business Acquisition, Goodwill, Expected Tax Deductible Amount | 51.3 |  |
Federal Government Business |  |  |
Goodwill [Roll Forward] |  |  |
Gross goodwill | 645.6 | 642.1 | 552.9
Goodwill, Purchase Accounting Adjustments | 3.5 |  |
Commercial Business |  |  |
Goodwill [Roll Forward] |  |  |
Gross goodwill | 829.9 | 778.6 | $ 738.4
Translation adjustment |  | (0.1) |
2020 Acquisitions |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill, Acquired During Period |  | 129.5 |
2020 Acquisitions | Federal Government Business |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill, Acquired During Period |  | 89.2 |
2020 Acquisitions | Commercial Business |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill, Acquired During Period |  | 40.3 |
2021 Acquisitions |  |  |
Goodwill [Roll Forward] |  |  |
Business Acquisition, Goodwill, Expected Tax Deductible Amount | 47.2 | $ 77.1 |
2021 Acquisitions | Commercial Business |  |  |
Goodwill [Roll Forward] |  |  |
Business Acquisition, Goodwill, Expected Tax Deductible Amount | 51.3 |  |
Accumulated Acquisition since 2019 |  |  |
Goodwill [Roll Forward] |  |  |
Business Acquisition, Goodwill, Expected Tax Deductible Amount | $ 124.3 |  |

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- 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=121556970&loc=d3e13816-109267 + Details
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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=121556970&loc=d3e13816-109267 + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=123586518&loc=d3e961-128460 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=121556970&loc=d3e13816-109267 + Details
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