INVESTMENTS (SCHEDULE OF INVESTMENT INCOME) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturities	$ 1,081.4	$ 1,090.1	$ 1,175.8
Equity securities	21.5	18.3	13.9
Mortgage loans	91.0	91.4	104.2
Policy loans	7.3	7.3	11.0
Other invested assets	24.3	17.4	17.1
Cash and cash equivalents	2.0	0.8	0.6
Trading securities	12.2	10.7	14.8
Option income (loss)	(40.1)	36.5	118.9
Change in value of options	69.3	(72.7)	(49.4)
Other special-purpose portfolios	79.7	55.5	42.1
Gross investment income	1,348.6	1,255.3	1,449.0
Less investment expenses	23.4	21.7	21.6
Net investment income	1,325.2	1,233.6	1,427.4
Investment Income [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Increase (decrease) in trading securities	$ (0.2)	$ 0.4	$ 3.4