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Investments - Realized Investment Gains (Losses) (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2021 | Mar. 31, 2020
Gain (Loss) on Securities [Line Items] |  |
Net investment losses | $ (9.0) | $ (18.5)
Fixed maturity securities |  |
Gain (Loss) on Securities [Line Items] |  |
Net investment losses | (5.4) | 1.1
Equity securities |  |
Gain (Loss) on Securities [Line Items] |  |
Net investment losses | (2.7) | (14.7)
Short-term investments and other |  |
Gain (Loss) on Securities [Line Items] |  |
Net investment losses | $ (0.9) | $ (4.9)

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- Definition Amount of realized gain (loss) on investment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.3(a)) -URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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