Schedule IV - Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Life insurance in force
Life insurance in force gross amount	$ 577,735.3	$ 530,828.6	$ 486,887.5
Life insurance in force ceded to other companies	368,583.0	324,691.3	287,538.8
Life insurance in force assumed from other companies	999.5	1,028.6	1,059.5
Life insurance in force net amount	$ 210,151.8	$ 207,165.9	$ 200,408.2
Life insurance in force, percentage of amount assumed to net (as a percent)	0.50%	0.50%	0.50%
Premiums:
Premiums gross amount	$ 8,428.1	$ 6,928.3	$ 6,699.3
Premiums ceded to other companies	563.1	520.4	483.8
Premiums assumed from other companies	1.6	1.7	1.9
Premiums net amount	7,866.6	6,409.6	6,217.4
Life insurance and annuities
Premiums:
Premiums gross amount	6,424.8	5,055.8	4,945.7
Premiums ceded to other companies	407.5	359.9	320.7
Premiums assumed from other companies	1.6	1.7	1.9
Premiums net amount	6,018.9	4,697.6	4,626.9
Accident and health insurance
Premiums:
Premiums gross amount	2,003.3	1,872.5	1,753.6
Premiums ceded to other companies	155.6	160.5	163.1
Premiums net amount	$ 1,847.7	$ 1,712.0	$ 1,590.5