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Investment Securities (Insurance-Linked Securities Funds) (Details) - USD ($) $ in Millions | 6 Months Ended |  |  |
--- | --- | --- | --- | ---
Jun. 30, 2019 | Dec. 31, 2018 | Jun. 30, 2018 | Dec. 31, 2017
Investment [Line Items] |  |  |  |
Fair value investments | $ 2,483.0 | $ 2,328.7 | $ 2,275.4 | $ 3,208.3
Insurance-Linked Securities Funds |  |  |  |
Investment [Line Items] |  |  |  |
Fair value investments | $ 40.3 |  |  |
Minimum |  |  |  |
Investment [Line Items] |  |  |  |
Redemptions and advanced redemption notice period | 30 days |  |  |
Maximum |  |  |  |
Investment [Line Items] |  |  |  |
Redemptions and advanced redemption notice period | 90 days |  |  |

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- Definition Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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