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Equity Method Investments in Affiliates - Additional Information (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2018 | Jun. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Amortization expense during the period | $ 30.1 |  | $ 21.2 | $ 76.5 | $ 65.1 |
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |
Carrying value of equity method investment in affiliate | 3,055.3 |  |  | 3,055.3 |  | $ 3,304.7
Acquired Client Relationships |  |  |  |  |  |
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |
Finite-lived intangible, future amortization expense in 2018 | 100.0 |  |  | 100.0 |  |
Finite-lived intangible, future amortization expense in 2019 | 90.0 |  |  | 90.0 |  |
Finite-lived intangible, future amortization expense in 2020 | 60.0 |  |  | 60.0 |  |
Finite-lived intangible, future amortization expense in 2021 | 35.0 |  |  | 35.0 |  |
Finite-lived intangible, future amortization expense in 2022 | 35.0 |  |  | 35.0 |  |
Equity Method Investee |  |  |  |  |  |
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |
Carrying value of equity method investment in affiliate | 3,055.3 |  |  | 3,055.3 |  | $ 3,304.7
Equity Method Investee | Investment One |  |  |  |  |  |
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |
Impairment recognized on equity method investment in affiliate |  | $ 33.3 |  |  |  |
Impairment recognized on equity method investment in affiliate, net of tax |  | 25.0 |  |  |  |
Carrying value of equity method investment in affiliate |  | $ 0.0 |  |  |  |
Revenue from equity method investment in affiliate | 283.2 |  | 301.8 | 884.9 | 826.6 |
Net income from equity method investment in affiliate | 135.0 |  | 178.3 | 443.3 | 471.3 |
Equity Method Investee | Acquired Client Relationships |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Amortization expense during the period | 22.2 |  | $ 25.9 | 109.0 | $ 71.7 |
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |
Finite-lived intangible, future amortization expense in 2018 | 100.0 |  |  | 100.0 |  |
Finite-lived intangible, future amortization expense in 2019 | 90.0 |  |  | 90.0 |  |
Finite-lived intangible, future amortization expense in 2020 | 90.0 |  |  | 90.0 |  |
Finite-lived intangible, future amortization expense in 2021 | 90.0 |  |  | 90.0 |  |
Finite-lived intangible, future amortization expense in 2022 | $ 90.0 |  |  | $ 90.0 |  |

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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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -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 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -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 + Details
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- Definition This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 35 -Paragraph 32 -URI http://asc.fasb.org/extlink&oid=114001220&loc=d3e32787-111569 + Details
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- Definition The amount of revenue from sale of goods and services reduced by sales returns, allowances, and discounts reported by an equity method investment of the entity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721683-107760 + Details
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