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Marketable Securities - Schedule of Fair Value and Unrealized Losses of Debt Securities (Details) - USD ($) $ in Millions | Sep. 30, 2020 | Dec. 31, 2019
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Debt Securities, Available-for-sale [Line Items] |  |
Fair Value - Less than 12 Months | $ 606.0 | $ 274.5
Unrealized Loss - Less than 12 months | (0.8) | (0.3)
Fair Value - 12 Months or Greater | 0.0 | 0.0
Unrealized Loss - 12 Months or Greater | 0.0 | 0.0
Fair Value - Total | 606.0 | 274.5
Unrealized Loss - Total | (0.8) | (0.3)
Corporate bonds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value - Less than 12 Months | 560.5 | 257.2
Unrealized Loss - Less than 12 months | (0.7) | (0.2)
Fair Value - 12 Months or Greater | 0.0 | 0.0
Unrealized Loss - 12 Months or Greater | 0.0 | 0.0
Fair Value - Total | 560.5 | 257.2
Unrealized Loss - Total | (0.7) | (0.2)
U.S. government and government agency obligations |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value - Less than 12 Months | 45.5 | 17.3
Unrealized Loss - Less than 12 months | (0.1) | (0.1)
Fair Value - 12 Months or Greater | 0.0 | 0.0
Unrealized Loss - 12 Months or Greater | 0.0 | 0.0
Fair Value - Total | 45.5 | 17.3
Unrealized Loss - Total | $ (0.1) | $ (0.1)

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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922890-210455 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27337-111563 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=121590138&loc=SL82922954-210456 + Details
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- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922890-210455 + Details
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