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Fair Value Measurements - Fair Value of Financial Assets and Liabilities Measured on a Recurring Basis (Details) - Fair Value Measured on a Recurring Basis - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Financial Assets |  |  |
Cash equivalents |  | $ 40.4 | $ 64.1
Investments in marketable securities |  |  |
Trading | [1] | 57.2 | 40.5
Available-for-sale securities | [1] | 20.6 | 81.9
Other investments |  |  | 3.4
Foreign currency forward contracts | [2] | 0.2 | 0.6
Financial Liabilities |  |  |
Contingent payment arrangements | [2] | 9.4 | 8.6
Affiliate equity obligations | [2] | 49.2 | 12.1
Foreign currency forward contracts | [2] | 0.6 | 0.5
Level 1 |  |  |
Financial Assets |  |  |
Cash equivalents |  | 40.4 | 64.1
Investments in marketable securities |  |  |
Trading | [1] | 57.2 | 40.5
Available-for-sale securities | [1] | 20.6 | 81.9
Other investments |  |  | 3.4
Foreign currency forward contracts | [2] | 0.0 | 0.0
Financial Liabilities |  |  |
Contingent payment arrangements | [2] | 0.0 | 0.0
Affiliate equity obligations | [2] | 0.0 | 0.0
Foreign currency forward contracts | [2] | 0.0 | 0.0
Level 2 |  |  |
Financial Assets |  |  |
Cash equivalents |  | 0.0 | 0.0
Investments in marketable securities |  |  |
Trading | [1] | 0.0 | 0.0
Available-for-sale securities | [1] | 0.0 | 0.0
Other investments |  |  | 0.0
Foreign currency forward contracts | [2] | 0.2 | 0.6
Financial Liabilities |  |  |
Contingent payment arrangements | [2] | 0.0 | 0.0
Affiliate equity obligations | [2] | 0.0 | 0.0
Foreign currency forward contracts | [2] | 0.6 | 0.5
Level 3 |  |  |
Financial Assets |  |  |
Cash equivalents |  | 0.0 | 0.0
Investments in marketable securities |  |  |
Trading | [1] | 0.0 | 0.0
Available-for-sale securities | [1] | 0.0 | 0.0
Other investments |  |  | 0.0
Foreign currency forward contracts | [2] | 0.0 | 0.0
Financial Liabilities |  |  |
Contingent payment arrangements | [2] | 9.4 | 8.6
Affiliate equity obligations | [2] | 49.2 | 12.1
Foreign currency forward contracts | [2] | $ 0.0 | $ 0.0
[1] | Principally investments in equity securities.
[2] | Amounts are presented within Other assets or Other liabilities.

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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562 + Details
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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
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