Segment Information - Additional Significant Financial Information by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information
DAC unlocking and amortization expense	$ 94.7	$ 99.9	$ 109.2
Income tax expense (benefit)	32.1	26.3	52.0
Property & Casualty | Operating Segments
Segment Reporting Information
DAC unlocking and amortization expense	67.7	74.4	79.5
Income tax expense (benefit)	13.2	15.4	14.0
Supplemental | Operating Segments
Segment Reporting Information
DAC unlocking and amortization expense	1.2	1.3	0.4
Income tax expense (benefit)	12.7	12.0	5.1
Retirement | Operating Segments
Segment Reporting Information
DAC unlocking and amortization expense	18.5	16.7	21.5
Income tax expense (benefit)	9.9	2.1	33.8
Life | Operating Segments
Segment Reporting Information
DAC unlocking and amortization expense	7.3	7.5	7.8
Income tax expense (benefit)	3.6	2.4	4.9
Corporate & Other | Corporate and Other
Segment Reporting Information
Income tax expense (benefit)	$ (7.3)	$ (5.6)	$ (5.8)