Investments - Net Investment Income (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net Investment Income
Total net investment income	$ 422.5	$ 357.6	$ 365.1
Investment Portfolio
Net Investment Income
Investment expenses	(10.1)	(9.6)	(9.4)
Total net investment income	321.4	260.3	294.3
Deposit Asset On Reinsurance
Net Investment Income
Total net investment income	101.1	97.3	70.8
Fixed maturity securities \| Investment Portfolio
Net Investment Income
Investment income	235.6	232.9	283.2
Equity securities \| Investment Portfolio
Net Investment Income
Investment income	5.3	4.7	4.9
Limited partnership interests \| Investment Portfolio
Net Investment Income
Investment income	79.0	20.9	25.7
Short-term and other investments \| Investment Portfolio
Net Investment Income
Investment income	$ 11.6	$ 11.4	$ (10.1)

Amount, before investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

+ References

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