Schedule 4 - Reinsurance Schedule (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Life Insurance in Force
Gross Amount	$ 19,706.2				$ 19,479.9				$ 19,706.2	$ 19,479.9	$ 19,435.1
Ceded to Other Companies	387.7				411.6				387.7	411.6	436.4
Assumed from Other Companies	152.3				162.8				152.3	162.8	172.7
Net Amount	$ 19,470.8				$ 19,231.1				$ 19,470.8	$ 19,231.1	$ 19,171.4
Percentage of Amount Assumed to Net	0.80%				0.80%				0.80%	0.80%	0.90%
Premiums
Gross Amount									$ 4,652.6	$ 4,407.5	$ 3,330.8
Ceded to Other Companies									31.2	27.4	31.6
Assumed from Other Companies									50.8	92.3	85.2
Net Amount	$ 1,214.0	$ 1,206.5	$ 1,085.3	$ 1,166.4	$ 1,145.8	$ 1,135.2	$ 1,116.6	$ 1,074.8	$ 4,672.2	$ 4,472.4	$ 3,384.4
Percentage of Amount Assumed to Net									1.10%	2.10%	2.50%
Life Insurance
Premiums
Gross Amount									$ 386.0	$ 383.6	$ 378.2
Ceded to Other Companies									1.1	1.2	1.2
Assumed from Other Companies									0.8	0.9	1.0
Net Amount									$ 385.7	$ 383.3	$ 378.0
Percentage of Amount Assumed to Net									0.20%	0.20%	0.30%
Accident and Health Insurance
Premiums
Gross Amount									$ 195.5	$ 188.5	$ 174.3
Ceded to Other Companies									1.6	1.7	1.7
Assumed from Other Companies									5.4	5.3	5.3
Net Amount									$ 199.3	$ 192.1	$ 177.9
Percentage of Amount Assumed to Net									2.70%	2.80%	3.00%
Property and Liability Insurance
Premiums
Gross Amount									$ 4,071.1	$ 3,835.4	$ 2,778.3
Ceded to Other Companies									28.5	24.5	28.7
Assumed from Other Companies									44.6	86.1	78.9
Net Amount									$ 4,087.2	$ 3,897.0	$ 2,828.5
Percentage of Amount Assumed to Net									1.10%	2.20%	2.80%