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Goodwill and Other Intangible Assets - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 01, 2017 | Jan. 01, 2017
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Goodwill impairment loss | $ 0.0 | $ 0.0 |  |  |
Amortization expense | 221.0 | 216.0 | $ 199.0 |  |
Internally developed software |  |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Disposal of fully amortized definite-lived intangible assets | $ 24.0 | $ 29.0 |  |  |
Corporate |  |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Fair values of reporting units, in excess of carrying value (as a percent) |  |  |  |  | 227.00%
Small Business |  |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Fair values of reporting units, in excess of carrying value (as a percent) |  |  |  |  | 308.00%
Public |  |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Fair values of reporting units, in excess of carrying value (as a percent) |  |  |  | 179.00% |
CANADA |  |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Fair values of reporting units, in excess of carrying value (as a percent) |  |  |  | 153.00% |

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- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
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- Definition Amount of loss from the write-down 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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13854-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13777-109266 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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