Schedule IV - Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Life insurance in force
Life insurance in force gross amount	$ 390,603.3	$ 354,951.9	$ 317,154.5
Life insurance in force ceded to other companies	184,588.9	177,418.6	144,024.9
Life insurance in force assumed from other companies	1,187.1	1,317.7	1,455.4
Life insurance in force net amount	$ 207,201.5	$ 178,851.0	$ 174,585.0
Life insurance in force, percentage of amount assumed to net (as a percent)	0.60%	0.70%	0.80%
Premiums:
Premiums gross amount	$ 5,710.8	$ 4,123.7	$ 3,524.8
Premiums ceded to other companies	402.4	402.9	373.2
Premiums assumed from other companies	1.9	2.1	2.5
Premiums net amount	5,310.3	$ 3,722.9	$ 3,154.1
Premiums percentage of amount assumed to net (as a percent)		0.10%	0.10%
Life insurance
Premiums:
Premiums gross amount	4,208.7	$ 2,725.4	$ 2,216.9
Premiums ceded to other companies	255.3	228.1	205.2
Premiums assumed from other companies	1.9	2.1	2.5
Premiums net amount	3,955.3	$ 2,499.4	$ 2,014.2
Premiums percentage of amount assumed to net (as a percent)		0.10%	0.10%
Accident and health insurance
Premiums:
Premiums gross amount	1,502.1	$ 1,398.3	$ 1,307.9
Premiums ceded to other companies	147.1	174.8	168.0
Premiums net amount	$ 1,355.0	$ 1,223.5	$ 1,139.9