Schedule IV – Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reinsurance [Line Items]
Life insurance in force, gross	$ 7,431.3	$ 8,270.1	$ 9,026.1
Life insurance in force, ceded to other companies	4,953.8	5,842.4	5,560.4
Life insurance in force, assumed other companies	2.5	3.8	2.8
Life insurance in force, net	$ 2,480.0	$ 2,431.5	$ 3,468.5
Life insurance in force, percentage of amount assumed to net	0.10%	0.20%	0.10%
Premiums, direct amount	$ 15,910.1	$ 14,912.0	$ 14,021.2
Premiums, ceded to other companies	7,506.5	6,769.5	6,275.2
Premiums, assumed from other companies	168.5	133.3	212.8
Net earned premiums	$ 8,572.1	$ 8,275.8	$ 7,958.8
Premiums, percentage of amount assumed to net	2.00%	1.60%	2.70%
Direct policyholder benefits	$ 6,271.4	$ 5,672.9	$ 5,534.9
Benefits, ceded to other companies	4,214.8	3,530.3	3,362.1
Benefits, assumed from other companies	139.1	122.3	212.9
Net policyholder benefits	$ 2,195.7	$ 2,264.9	$ 2,385.7
Benefits, percentage of amount assumed to net	6.30%	5.40%	8.90%
Life insurance
Reinsurance [Line Items]
Premiums, direct amount	$ 199.6	$ 172.9	$ 223.5
Premiums, ceded to other companies	161.0	128.9	175.9
Premiums, assumed from other companies	0.2	0.2	0.2
Net earned premiums	$ 38.8	$ 44.2	$ 47.8
Premiums, percentage of amount assumed to net	0.40%	0.40%	0.40%
Direct policyholder benefits	$ 180.6	$ 49.8	$ 67.9
Benefits, ceded to other companies	163.7	34.9	49.9
Benefits, assumed from other companies	0.0	(0.7)	(0.4)
Net policyholder benefits	$ 16.9	$ 14.2	$ 17.6
Benefits, percentage of amount assumed to net	(0.20%)	(4.60%)	(2.40%)
Accident and health insurance
Reinsurance [Line Items]
Premiums, direct amount	$ 539.4	$ 494.1	$ 538.3
Premiums, ceded to other companies	364.9	317.4	361.3
Premiums, assumed from other companies	1.4	0.2	0.3
Net earned premiums	$ 175.9	$ 176.9	$ 177.3
Premiums, percentage of amount assumed to net	0.80%	0.10%	0.20%
Direct policyholder benefits	$ 222.2	$ 161.6	$ 217.7
Benefits, ceded to other companies	205.0	111.2	193.5
Benefits, assumed from other companies	0.0	(4.0)	0.0
Net policyholder benefits	$ 17.2	$ 46.4	$ 24.2
Benefits, percentage of amount assumed to net	(0.30%)	(8.70%)	0.20%
Property and liability insurance
Reinsurance [Line Items]
Premiums, direct amount	$ 15,171.1	$ 14,245.0	$ 13,259.4
Premiums, ceded to other companies	6,980.6	6,323.2	5,738.0
Premiums, assumed from other companies	166.9	132.9	212.3
Net earned premiums	$ 8,357.4	$ 8,054.7	$ 7,733.7
Premiums, percentage of amount assumed to net	2.00%	1.60%	2.70%
Direct policyholder benefits	$ 5,868.6	$ 5,461.5	$ 5,249.3
Benefits, ceded to other companies	3,846.1	3,384.2	3,118.7
Benefits, assumed from other companies	139.1	127.0	213.3
Net policyholder benefits	$ 2,161.6	$ 2,204.3	$ 2,343.9
Benefits, percentage of amount assumed to net	6.40%	5.80%	9.10%