Investments - Net Investment (Losses) Gains By Transaction Type (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Credit loss impairments	$ (0.9)	$ (1.1)
Intent-to-sell impairments	(0.9)	(2.1)
Total impairments on investments recognized in net income	(1.8)	(3.2)
Sales and other, net	1.1	(2.1)
Change in fair value - equity securities	(17.1)	(2.8)
Change in fair value and losses realized on settlements - derivatives	2.3	(0.9)
Net investment losses	(15.5)	(9.0)
Credit losses on fixed maturity securities for which credit losses were not previously reported	$ 0.9	$ 1.1

Other than Temporary Impairment Losses, Investments, Portion Recognized In Earnings, Change In Intent

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Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

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Amount of unrealized and realized gain (loss) on investment in debt and equity securities.

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Amount of expense for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), for which no credit loss was previously recorded.

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Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings.

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Amount of other-than-temporary impairment (OTTI) on investment in debt security, recognized in earnings.

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Amount of realized gain (loss) on investment.

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