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Investment Securities - Investment Gains and Losses For Level 3 (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Investment securities |  |  |
Unrealized investment gains (losses) | $ (313.4) | $ (395.2) | $ 529.7
Proceeds from sale and maturity of investments | 500.0 | 800.0 | 1,400.0
Level 3 |  |  |
Investment securities |  |  |
Unrealized investment gains | $ 56.5 | $ 98.9 | 276.0
MediaAlpha |  |  |
Investment securities |  |  |
Unrealized investment gains (losses) |  |  | $ 278.7

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- Definition Amount of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in net income (trading). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (e) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27357-111563 + Details
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- Definition The cash inflow from sales, maturities, prepayments, calls and collections of all investments, including securities and other assets, having ready marketability and intended by management to be liquidated, if necessary, beyond the current operating cycle. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3179-108585 + 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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- Definition Amount of unrealized gain (loss) on investment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585 + Details
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