Investments - Allowance for Credit Losses, Unrealized Losses on Securities (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Equity Securities
Investment Holdings [Line Items]
Unrealized gains (losses) on equity securities still held	$ 41.2	$ 115.2

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.

No definition available.

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