Schedule IV - Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Life insurance in force
Life insurance in force gross amount	$ 626,155.6	$ 577,735.3	$ 530,828.6
Life insurance in force ceded to other companies	377,308.2	368,583.0	324,691.3
Life insurance in force assumed from other companies	904.1	999.5	1,028.6
Life insurance in force net amount	$ 249,751.5	$ 210,151.8	$ 207,165.9
Life insurance in force, percentage of amount assumed to net (as a percent)	0.40%	0.50%	0.50%
Premiums:
Premiums gross amount	$ 6,645.4	$ 8,428.1	$ 6,928.3
Premiums ceded to other companies	609.7	563.1	520.4
Premiums assumed from other companies	1.7	1.6	1.7
Premiums net amount	6,037.4	7,866.6	6,409.6
Life insurance and annuities
Premiums:
Premiums gross amount	4,608.7	6,424.8	5,055.8
Premiums ceded to other companies	453.1	407.5	359.9
Premiums assumed from other companies	1.7	1.6	1.7
Premiums net amount	4,157.3	6,018.9	4,697.6
Accident and health insurance
Premiums:
Premiums gross amount	2,036.7	2,003.3	1,872.5
Premiums ceded to other companies	156.6	155.6	160.5
Premiums net amount	$ 1,880.1	$ 1,847.7	$ 1,712.0