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Equity-Method Eligible Investments (Balance Sheet and Income Statement Tables) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |  |
Assets | $ 3,983.2 |  |  |  | $ 3,362.6 |  |  |  | $ 3,983.2 | $ 3,362.6 |
Liabilities | 838.5 |  |  |  | 644.4 |  |  |  | 838.5 | 644.4 |
Revenues | 175.3 | $ 155.5 | $ 129.0 | $ 433.6 | 6.0 | $ 198.7 | $ 122.3 | $ 42.1 | 893.4 | 369.1 | $ 373.8
White Mountains |  |  |  |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |  |
Assets | 1,959.2 |  |  |  | 1,373.3 |  |  |  | 1,959.2 | 1,373.3 |
Liabilities | 653.2 |  |  |  | 509.2 |  |  |  | 653.2 | 509.2 |
Revenues |  |  |  |  |  |  |  |  | 344.6 | 226.0 | 143.3
Expenses |  |  |  |  |  |  |  |  | 88.3 | 141.4 | 80.5
Net Income |  |  |  |  |  |  |  |  | 255.1 | 83.6 | 65.3
MediaAlpha |  |  |  |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |  |
Assets | 106.9 |  |  |  | 88.5 |  |  |  | 106.9 | 88.5 |
Liabilities | $ 144.6 |  |  |  | $ 46.9 |  |  |  | 144.6 | 46.9 |
Revenues |  |  |  |  |  |  |  |  | 407.9 | 297.1 | 163.2
Expenses |  |  |  |  |  |  |  |  | 389.0 | 288.2 | 163.5
Net Income |  |  |  |  |  |  |  |  | $ 18.9 | $ 8.9 | $ (0.3)

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