ACCOUNTING FOR DERIVATIVES - SCHEDULE PRE-TAX GAINS (LOSSES) RECOGNIZED IN NET INCOME FOR DERIVATIVE INSTRUMENTS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative [Line Items]
Gains (losses) on derivatives not designated as hedging instruments	$ 51.8	$ (26.9)	$ (19.6)	$ (34.4)
Net investment income (loss) from policyholder and other special-purpose portfolios: | Fixed index call options
Derivative [Line Items]
Gains (losses) on derivatives not designated as hedging instruments	45.0	3.6	(37.7)	68.8
Net realized gains (losses) | Embedded derivative | Coinsurance agreements
Derivative [Line Items]
Gains (losses) on derivatives not designated as hedging instruments	1.7	1.6	1.8	6.5
Insurance policy benefits | Embedded derivative | Fixed index annuities
Derivative [Line Items]
Gains (losses) on derivatives not designated as hedging instruments	$ 5.1	$ (32.1)	$ 16.3	$ (109.7)