SCHEDULE II - STATEMENT OF OPERATIONS (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Net investment income									$ 1,325.2	$ 1,233.6	$ 1,427.4
Net realized investment gains (losses)									8.3	(36.6)	33.9
Total revenues	$ 1,004.9	$ 1,015.9	$ 1,003.9	$ 960.4	$ 969.6	$ 904.5	$ 959.5	$ 978.3	3,985.1	3,811.9	4,144.7
Expenses:
Interest expense									116.4	94.9	92.8
Loss on extinguishment or modification of debt									0.0	32.8	0.6
Income before income taxes	180.7	49.3	82.7	40.5	160.3	52.4	72.7	82.3	353.2	367.7	175.1
Income tax expense	(53.5)	30.7	22.8	(5.0)	23.0	18.6	25.9	29.5	(5.0)	97.0	123.7
Net income	$ 234.2	$ 18.6	$ 59.9	$ 45.5	$ 137.3	$ 33.8	$ 46.8	$ 52.8	358.2	270.7	51.4
Parent Company [Member]
Revenues:
Net investment income									15.6	16.9	12.7
Net realized investment gains (losses)									17.7	3.5	11.1
Intercompany losses (eliminated in consolidation)									0.0	(1.5)	(1.0)
Total revenues									33.3	18.9	22.8
Expenses:
Interest expense									45.8	45.2	44.0
Intercompany expenses (eliminated in consolidation)									0.9	0.4	0.3
Operating costs and expenses									48.2	21.0	66.6
Loss on extinguishment or modification of debt									0.0	32.8	0.6
Total expenses									94.9	99.4	111.5
Income before income taxes									(61.6)	(80.5)	(88.7)
Income tax expense									(54.6)	(37.9)	(34.1)
Loss before equity in undistributed earnings of subsidiaries									(7.0)	(42.6)	(54.6)
Equity in undistributed earnings of subsidiaries (eliminated in consolidation)									365.2	313.3	106.0
Net income									$ 358.2	$ 270.7	$ 51.4