FAIR VALUE MEASUREMENTS (FAIR VALUE ASSETS AND LIABILITIES MEASURED ON A RECURRING BASIS, UNOBSERVABLE INPUT RECONCILIATION) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Future policy benefits - embedded derivatives associated with fixed index annuity products [Member]
Liabilities:
Beginning balance	$ (1,057.1)	$ (1,081.5)
Purchases, sales, issuances and settlements, net	(96.0)	(11.9)
Total realized and unrealized gains (losses) included in net income	60.8	36.3
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	0.0	0.0
Transfers into level 3	0.0	0.0
Transfers out of level 3	0.0	0.0
Ending balance	(1,092.3)	(1,057.1)
Amount of total gains (losses) for the year included in our net income related to liabilities still held as of the reporting date	60.8	36.3
Corporate securities [Member]
Assets:
Beginning balance	170.4	365.9
Purchases, sales, issuances and settlements, net	76.5	31.0
Total realized and unrealized gains (losses) included in net income	(10.7)	(2.2)
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	9.1	(19.5)
Transfers into level 3	20.3	37.4
Transfers out of level 3	(7.1)	(242.2)
Ending balance	258.5	170.4
Amount of total gains (losses) for the year included in our net income relating to assets still held as of the reporting date	(10.9)	0.0
States and political subdivisions [Member]
Assets:
Beginning balance	0.0	35.5
Purchases, sales, issuances and settlements, net		(35.5)
Total realized and unrealized gains (losses) included in net income		0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)		0.0
Transfers into level 3		0.0
Transfers out of level 3		0.0
Ending balance		0.0
Amount of total gains (losses) for the year included in our net income relating to assets still held as of the reporting date		0.0
Foreign Government Debt Securities [Member]
Assets:
Beginning balance	0.0
Purchases, sales, issuances and settlements, net	4.0
Total realized and unrealized gains (losses) included in net income	0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	(0.1)
Transfers into level 3	0.0
Transfers out of level 3	0.0
Ending balance	3.9	0.0
Amount of total gains (losses) for the year included in our net income relating to assets still held as of the reporting date	0.0
Asset-backed securities [Member]
Assets:
Beginning balance	35.9	59.2
Purchases, sales, issuances and settlements, net	9.7	6.7
Total realized and unrealized gains (losses) included in net income	0.0	0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	2.2	(1.4)
Transfers into level 3	26.3	0.0
Transfers out of level 3	(13.7)	(28.6)
Ending balance	60.4	35.9
Amount of total gains (losses) for the year included in our net income relating to assets still held as of the reporting date	0.0	0.0
Collateralized debt obligations [Member]
Assets:
Beginning balance	0.0
Purchases, sales, issuances and settlements, net	5.4
Total realized and unrealized gains (losses) included in net income	0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	0.0
Transfers into level 3	0.0
Transfers out of level 3	0.0
Ending balance	5.4	0.0
Amount of total gains (losses) for the year included in our net income relating to assets still held as of the reporting date	0.0
Commercial Mortgage Backed Securities [Member]
Assets:
Beginning balance	1.1	1.2
Purchases, sales, issuances and settlements, net	16.9	(0.1)
Total realized and unrealized gains (losses) included in net income	0.0	0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	0.1	0.0
Transfers into level 3	13.9	0.0
Transfers out of level 3	0.0	0.0
Ending balance	32.0	1.1
Amount of total gains (losses) for the year included in our net income relating to assets still held as of the reporting date	0.0	0.0
Mortgage pass-through securities [Member]
Assets:
Beginning balance	0.1	0.4
Purchases, sales, issuances and settlements, net	(0.1)	(0.3)
Total realized and unrealized gains (losses) included in net income	0.0	0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	0.0	0.0
Transfers into level 3	0.0	0.0
Transfers out of level 3	0.0	0.0
Ending balance	0.0	0.1
Amount of total gains (losses) for the year included in our net income relating to assets still held as of the reporting date	0.0	0.0
Total fixed maturities, available for sale [Member]
Assets:
Beginning balance	207.5	462.2
Purchases, sales, issuances and settlements, net	112.4	1.8
Total realized and unrealized gains (losses) included in net income	(10.7)	(2.2)
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	11.3	(20.9)
Transfers into level 3	60.5	37.4
Transfers out of level 3	(20.8)	(270.8)
Ending balance	360.2	207.5
Amount of total gains (losses) for the year included in our net income relating to assets still held as of the reporting date	(10.9)	0.0
Equity securities - corporate securities [Member]
Assets:
Beginning balance	32.0	28.0
Purchases, sales, issuances and settlements, net	5.5	4.0
Total realized and unrealized gains (losses) included in net income	(12.7)	0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	0.4	0.0
Transfers into level 3	0.0	0.0
Transfers out of level 3	0.0	0.0
Ending balance	25.2	32.0
Amount of total gains (losses) for the year included in our net income relating to assets still held as of the reporting date	(12.7)	0.0
Trading securities - commercial mortgage-backed securities [Member]
Assets:
Beginning balance	39.9	28.6
Purchases, sales, issuances and settlements, net	0.0	9.5
Total realized and unrealized gains (losses) included in net income	0.0	0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	0.0	1.8
Transfers into level 3	0.0	0.0
Transfers out of level 3	(39.9)	0.0
Ending balance	0.0	39.9
Amount of total gains (losses) for the year included in our net income relating to assets still held as of the reporting date	$ 0.0	$ 1.8