Basis of Presentation and Significant Accounting Policies - Deferred Policy Acquisition Costs (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information
Deferred policy acquisition costs	$ 248.0	$ 229.8
Property & Casualty
Segment Reporting Information
Deferred policy acquisition costs	24.4	26.1
Supplemental
Segment Reporting Information
Deferred policy acquisition costs	4.2	4.3
Retirement
Segment Reporting Information
Deferred policy acquisition costs	153.8	137.7
Life
Segment Reporting Information
Deferred policy acquisition costs	$ 65.6	$ 61.7