Schedule IV Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Life insurance in force
Gross Amount	$ 40,422.9	$ 38,564.6	$ 21,032.6
Ceded to Other Companies	9,597.7	9,330.9	4,693.5
Assumed from Other Companies	0.0	0.0	0.0
Net Amount	$ 30,825.2	$ 29,233.7	$ 16,339.1
Percentage of Amount Assumed to Net	0.00%	0.00%	0.00%
Premiums
Gross Amount	$ 1,097.6	$ 1,046.7	$ 912.4
Ceded to Other Companies	76.3	72.0	33.3
Assumed from Other Companies	35.8	53.0	9.7
Net Amount	$ 1,057.1	$ 1,027.7	$ 888.8
Percentage of Amount Assumed to Net	3.40%	5.20%	1.10%
Property & Casualty
Premiums
Gross Amount	$ 653.0	$ 614.7	$ 623.0
Ceded to Other Companies	18.1	15.0	15.3
Assumed from Other Companies	10.7	8.5	9.7
Net Amount	$ 645.6	$ 608.2	$ 617.4
Percentage of Amount Assumed to Net	1.70%	1.40%	1.60%
Life & Retirement
Premiums
Gross Amount	$ 166.5	$ 158.9	$ 159.5
Ceded to Other Companies	14.8	14.9	16.1
Assumed from Other Companies	0.0	0.0	0.0
Net Amount	$ 151.7	$ 144.0	$ 143.4
Percentage of Amount Assumed to Net	0.00%	0.00%	0.00%
Supplemental & Group Benefits
Premiums
Gross Amount	$ 278.1	$ 273.1	$ 129.9
Ceded to Other Companies	43.4	42.1	1.9
Assumed from Other Companies	25.1	44.5	0.0
Net Amount	$ 259.8	$ 275.5	$ 128.0
Percentage of Amount Assumed to Net	9.70%	16.20%	0.00%