Schedule 4 - Reinsurance Schedule (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Life Insurance in Force
Gross Amount	$ 19,479.9				$ 19,435.1				$ 19,479.9	$ 19,435.1	$ 19,208.7
Ceded to Other Companies	411.6				436.4				411.6	436.4	455.2
Assumed from Other Companies	162.8				172.7				162.8	172.7	184.0
Net Amount	$ 19,231.1				$ 19,171.4				$ 19,231.1	$ 19,171.4	$ 18,937.5
Percentage of Amount Assumed to Net	0.80%				0.90%				0.80%	0.90%	1.00%
Premiums
Gross Amount									$ 4,407.5	$ 3,330.8	$ 2,295.3
Ceded to Other Companies									27.4	31.6	18.2
Assumed from Other Companies									92.3	85.2	72.9
Net Amount	$ 1,145.8	$ 1,135.2	$ 1,116.6	$ 1,074.8	$ 1,063.6	$ 1,052.9	$ 658.1	$ 609.8	$ 4,472.4	$ 3,384.4	$ 2,350.0
Percentage of Amount Assumed to Net									2.10%	2.50%	3.10%
Life Insurance
Premiums
Gross Amount									$ 383.6	$ 378.2	$ 366.8
Ceded to Other Companies									1.2	1.2	1.4
Assumed from Other Companies									0.9	1.0	1.1
Net Amount									$ 383.3	$ 378.0	$ 366.5
Percentage of Amount Assumed to Net									0.20%	0.30%	0.30%
Accident and Health Insurance
Premiums
Gross Amount									$ 188.5	$ 174.3	$ 171.0
Ceded to Other Companies									1.7	1.7	1.5
Assumed from Other Companies									5.3	5.3	5.4
Net Amount									$ 192.1	$ 177.9	$ 174.9
Percentage of Amount Assumed to Net									2.80%	3.00%	3.10%
Property and Liability Insurance
Premiums
Gross Amount									$ 3,835.4	$ 2,778.3	$ 1,757.5
Ceded to Other Companies									24.5	28.7	15.3
Assumed from Other Companies									86.1	78.9	66.4
Net Amount									$ 3,897.0	$ 2,828.5	$ 1,808.6
Percentage of Amount Assumed to Net									2.20%	2.80%	3.70%