Schedule 4 - Reinsurance Schedule (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021
Life Insurance in Force
Gross Amount	$ 19,750.8	$ 19,885.1		$ 20,287.7
Ceded to Other Companies	339.4	354.8		372.3
Assumed from Other Companies	129.9	137.1		144.5
Net Amount	$ 19,541.3	$ 19,667.4		$ 20,059.9
Percentage of Amount Assumed to Net	0.70%	0.70%		0.70%
Premiums
Gross Amount	$ 4,532.4	$ 5,229.8		$ 5,180.6
Ceded to Other Companies	32.7	42.7		36.1
Assumed from Other Companies	29.7	26.3		34.7
Net Amount	$ 4,529.4	$ 5,213.4	[1]	$ 5,179.2	[1]
Percentage of Amount Assumed to Net	0.70%	0.50%		0.70%
Life Insurance
Premiums
Gross Amount	$ 322.0	$ 355.8		$ 327.4
Ceded to Other Companies	3.3	3.6		0.9
Assumed from Other Companies	0.5	0.6		0.7
Net Amount	$ 319.2	$ 352.8		$ 327.2
Percentage of Amount Assumed to Net	0.20%	0.20%		0.20%
Accident and Health Insurance
Premiums
Gross Amount	$ 34.7	$ 167.9		$ 185.8
Ceded to Other Companies	11.6	1.1		0.3
Assumed from Other Companies	0.0	1.4		4.4
Net Amount	$ 23.1	$ 168.2		$ 189.9
Percentage of Amount Assumed to Net	0.00%	0.80%		2.30%
Property and Liability Insurance
Premiums
Gross Amount	$ 4,175.7	$ 4,706.1		$ 4,667.4
Ceded to Other Companies	17.8	38.0		34.9
Assumed from Other Companies	29.2	24.3		29.6
Net Amount	$ 4,187.1	$ 4,692.4		$ 4,662.1
Percentage of Amount Assumed to Net	0.70%	0.50%		0.60%

[1] As of January 1, 2023, the Company adopted ASU 2018-12 using the modified retrospective method applied as of the transition date of January 1, 2021. Prior period amounts in the financial statements have been recast to reflect application of the new guidance. See Note 2 to the Consolidated Financial Statements for additional information.