Insurance Liabilities - Claims Development Tables (Details) $ in Millions	Dec. 31, 2022 USD ($) claim	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Claims Development
Total outstanding liabilities for unpaid claims net of reinsurance	$ 1,393.2
Long-Term Disability/Group Life Waiver
Claims Development
Net incurred claims	2,268.6
Net cumulative paid claims	1,267.8
Liability for unpaid claims net, not separately presented	239.5
Total outstanding liabilities for unpaid claims net of reinsurance	1,240.3
Long-Term Disability/Group Life Waiver | Incurral year 2013
Claims Development
Net incurred claims	174.5	$ 174.5	$ 173.4	$ 177.1	$ 179.5	$ 182.3	$ 190.7	$ 188.4	$ 203.3	$ 219.3
Incurred but not reported claims	$ 0.1
Cumulative number of reported claims | claim	7,051
Net cumulative paid claims	$ 139.6	134.9	129.0	123.2	116.4	106.4	97.0	81.4	55.0	$ 12.5
Long-Term Disability/Group Life Waiver | Incurral year 2014
Claims Development
Net incurred claims	199.8	199.3	202.0	201.9	206.2	218.1	214.4	231.4	242.2
Incurred but not reported claims	$ 0.1
Cumulative number of reported claims | claim	7,604
Net cumulative paid claims	$ 153.3	147.2	140.8	132.4	122.3	111.8	96.3	66.0	$ 16.1
Long-Term Disability/Group Life Waiver | Incurral year 2015
Claims Development
Net incurred claims	210.5	211.8	210.0	208.2	215.3	217.2	227.2	231.0
Incurred but not reported claims	$ 0.1
Cumulative number of reported claims | claim	7,181
Net cumulative paid claims	$ 154.0	146.5	137.1	126.8	114.6	98.0	67.0	$ 16.9
Long-Term Disability/Group Life Waiver | Incurral year 2016
Claims Development
Net incurred claims	221.9	218.7	214.4	219.5	219.4	228.4	229.8
Incurred but not reported claims	$ 0.1
Cumulative number of reported claims | claim	6,167
Net cumulative paid claims	$ 157.1	147.2	136.8	124.9	105.6	70.6	$ 16.2
Long-Term Disability/Group Life Waiver | Incurral year 2017
Claims Development
Net incurred claims	246.5	245.2	245.8	243.1	239.7	238.4
Incurred but not reported claims	$ 0.1
Cumulative number of reported claims | claim	6,082
Net cumulative paid claims	$ 165.4	151.7	135.9	115.0	76.5	$ 17.8
Long-Term Disability/Group Life Waiver | Incurral year 2018
Claims Development
Net incurred claims	235.3	239.8	239.2	245.1	239.4
Incurred but not reported claims	$ 0.1
Cumulative number of reported claims | claim	5,774
Net cumulative paid claims	$ 150.3	135.7	115.7	79.9	$ 20.1
Long-Term Disability/Group Life Waiver | Incurral year 2019
Claims Development
Net incurred claims	240.2	240.4	248.4	255.2
Incurred but not reported claims	$ 5.7
Cumulative number of reported claims | claim	5,945
Net cumulative paid claims	$ 136.4	117.5	79.7	$ 19.2
Long-Term Disability/Group Life Waiver | Incurral year 2020
Claims Development
Net incurred claims	221.1	231.0	252.1
Incurred but not reported claims	$ 8.4
Cumulative number of reported claims | claim	5,913
Net cumulative paid claims	$ 113.1	78.8	$ 20.6
Long-Term Disability/Group Life Waiver | Incurral year 2021
Claims Development
Net incurred claims	244.5	259.7
Incurred but not reported claims	$ 4.0
Cumulative number of reported claims | claim	5,484
Net cumulative paid claims	$ 79.0	19.8
Long-Term Disability/Group Life Waiver | Incurral year 2022
Claims Development
Net incurred claims	274.3
Incurred but not reported claims	$ 109.8
Cumulative number of reported claims | claim	3,422
Net cumulative paid claims	$ 19.6
Dental/Vision/Short Term Disability/Critical Illness/Accident/PFML Claims
Claims Development
Net incurred claims	1,738.5
Net cumulative paid claims	1,658.8
Total outstanding liabilities for unpaid claims net of reinsurance	79.7
Dental/Vision/Short Term Disability/Critical Illness/Accident/PFML Claims | Incurral year 2021
Claims Development
Net incurred claims	$ 814.1	826.0
Cumulative number of reported claims | claim	3,749,753
Net cumulative paid claims	$ 813.3	753.4
Dental/Vision/Short Term Disability/Critical Illness/Accident/PFML Claims | Incurral year 2022
Claims Development
Net incurred claims	924.4
Incurred but not reported claims	$ 56.5
Cumulative number of reported claims | claim	4,114,456
Net cumulative paid claims	$ 845.5
Group Life
Claims Development
Net incurred claims	600.8
Net cumulative paid claims	532.6
Liability for unpaid claims net, not separately presented	5.0
Total outstanding liabilities for unpaid claims net of reinsurance	73.2
Group Life | Incurral year 2021
Claims Development
Net incurred claims	321.5	317.6
Incurred but not reported claims	$ 0.8
Cumulative number of reported claims | claim	7,079
Net cumulative paid claims	$ 314.3	$ 243.9
Group Life | Incurral year 2022
Claims Development
Net incurred claims	279.3
Incurred but not reported claims	$ 24.7
Cumulative number of reported claims | claim	5,368
Net cumulative paid claims	$ 218.3