ACCOUNTING FOR DERIVATIVES - FAIR VALUE BY BALANCE SHEET LOCATION (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fixed index call options
Derivatives, Fair Value [Line Items]
Assets	$ 143.5	$ 170.2
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Assets	137.1	168.8
Liabilities	1,370.0	1,334.8
Not Designated as Hedging Instrument | Fixed index call options | Other invested assets:
Derivatives, Fair Value [Line Items]
Assets	143.5	170.2
Not Designated as Hedging Instrument | Reinsurance receivables | Other invested assets:
Derivatives, Fair Value [Line Items]
Assets	(6.4)	(1.4)
Not Designated as Hedging Instrument | Fixed index products | Future policy benefits:
Derivatives, Fair Value [Line Items]
Liabilities	$ 1,370.0	$ 1,334.8