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Fair Value (Available-For-Sale Securities) (Details) - USD ($) $ in Millions | Sep. 30, 2016 | Dec. 31, 2015
--- | --- | ---
Fair Value Disclosure [Line Items] |  |
Amortized Cost | $ 134.5 | $ 129.4
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 2.8 | 0.4
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax | (0.2) | (1.1)
Fair Value | 137.1 | 128.7
U.S. Treasury securities |  |
Fair Value Disclosure [Line Items] |  |
Amortized Cost | 37.4 | 33.7
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax | 0.9 | 0.1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | 0.0 | (0.3)
Fair Value | 38.3 | 33.5
Corporate/Other Debt Securities |  |
Fair Value Disclosure [Line Items] |  |
Amortized Cost | 97.1 | 95.7
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax | 1.9 | 0.3
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | (0.2) | (0.8)
Fair Value | $ 98.8 | $ 95.2

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- Definition Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563 + Details
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- Definition Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563 + Details
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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=65884222&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=73527792&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=66010992&loc=d3e26610-111562 + Details
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