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Investments - Carrying Amount of Equity Method Limited Partnership Interests (Details) - USD ($) $ in Millions | Jun. 30, 2021 | Dec. 31, 2020
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Schedule of Equity Method Investments [Line Items] |  |
Limited partnership interests | $ 585.7 | $ 449.0
Senior commercial mortgage loan funds |  |
Schedule of Equity Method Investments [Line Items] |  |
Limited partnership interests | 254.8 | 149.6
Hedge funds |  |
Schedule of Equity Method Investments [Line Items] |  |
Limited partnership interests | 50.7 | 63.2
Infrastructure debt funds |  |
Schedule of Equity Method Investments [Line Items] |  |
Limited partnership interests | 58.1 | 58.3
Infrastructure equity funds |  |
Schedule of Equity Method Investments [Line Items] |  |
Limited partnership interests | 57.3 | 52.1
Other |  |
Schedule of Equity Method Investments [Line Items] |  |
Limited partnership interests | $ 164.8 | $ 125.8

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