INVESTMENTS IN VARIABLE INTEREST ENTITIES (SUPPLEMENTAL INFORMATION, REVENUES AND EXPENSES OF VARIABLE INTEREST ENTITIES) (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:
Policyholder and reinsurer accounts and other special-purpose portfolios									$ 121.1	$ 30.0	$ 126.4
Fee revenue and other income									50.5	58.9	50.9
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
Other operating costs and expenses									796.3	739.2	802.8
Total benefits and expenses									3,631.9	3,444.2	3,969.6
Net realized investment losses									8.3	(36.6)	33.9
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
Variable Interest Entity, Primary Beneficiary [Member]
Revenues:
Policyholder and reinsurer accounts and other special-purpose portfolios									78.9	62.1	47.2
Fee revenue and other income									6.4	1.6	1.1
Total revenues									85.3	63.7	48.3
Expenses:
Interest expense									53.1	38.8	30.1
Other operating costs and expenses									1.5	2.0	1.2
Total benefits and expenses									54.6	40.8	31.3
Income before net realized investment losses and income taxes									30.7	22.9	17.0
Net realized investment losses									(20.4)	(6.4)	(2.2)
Income before income taxes									$ 10.3	$ 16.5	$ 14.8