Investments - Change in Allowance for Credit Losses on Fixed Maturities Available-for-Sale (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning of the Year	$ 3.3	$ 0.0
Impact of Adopting ASU 2016-13		0.0
Additions for Securities for which No Previous Expected Credit Losses were Recognized	5.6	7.1
Reduction Due to Sales	0.0	(2.0)
Net Increase (Decrease) in Allowance on Securities for which Expected Credit Losses were Previously Recognized	(1.1)	(0.4)
Write-offs Charged Against Allowance	(0.3)	(1.4)
End of Year	7.5	3.3
Foreign Governments
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning of the Year	0.3	0.0
Impact of Adopting ASU 2016-13		0.0
Additions for Securities for which No Previous Expected Credit Losses were Recognized	0.0	1.2
Reduction Due to Sales	0.0	(0.7)
Net Increase (Decrease) in Allowance on Securities for which Expected Credit Losses were Previously Recognized	(0.3)	(0.2)
Write-offs Charged Against Allowance	0.0
End of Year	0.0	0.3
Corporate Bonds and Notes
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning of the Year	3.0	0.0
Impact of Adopting ASU 2016-13		0.0
Additions for Securities for which No Previous Expected Credit Losses were Recognized	5.6	5.9
Reduction Due to Sales	0.0	(1.3)
Net Increase (Decrease) in Allowance on Securities for which Expected Credit Losses were Previously Recognized	(0.8)	(0.2)
Write-offs Charged Against Allowance	(0.3)	(1.4)
End of Year	$ 7.5	$ 3.0