BUSINESS SEGMENTS - SCHEDULE OF SEGMENT REPORTING INFORMATION BY SEGMENT (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenues:
Insurance policy income	$ 2,499.8	$ 2,523.4	$ 2,511.3
Net investment income	1,015.9	1,420.7	1,222.5
Fee revenue and other income	196.5	159.0	123.5
Total segment revenues	3,667.0	4,076.1	3,807.5
Benefits and expenses:
Insurance policy benefits	1,658.3	2,190.7	2,157.9
Interest credited
Interest expense	137.0	95.4	108.8
Other operating costs and expenses	954.6	987.3	942.0
Total segment expenses	3,309.9	3,605.5	3,343.7
Operating earnings before taxes	357.1	470.6	463.8
Income tax expense on operating income	83.2	105.0	101.5
Net operating income	273.9	365.6	362.3
Insurance Product Lines
Benefits and expenses:
Allocated expenses	596.6	566.5	557.7
Total insurance product margin	811.3	913.7	921.5
Operating earnings before taxes	214.7	347.2	363.8
Investments not allocated to product lines
Revenues:
Change in market values of the underlying options supporting the fixed indexed annuity and life products (offset by market value changes credited to policyholder balances)	(205.3)	219.8	37.8
Investment income not allocated to product lines	272.1	273.3	258.5
Benefits and expenses:
Interest credited	28.5	2.2	0.0
Amortization	1.5	0.1	0.0
Market value changes of options credited to fixed indexed annuity and life policyholders	(205.3)	219.8	37.8
Interest expense	96.0	72.2	76.4
Other operating costs and expenses	(13.4)	16.6	15.0
Total insurance product margin	159.5	184.5	167.1
Assets of our other non-life companies
Revenues:
Fee revenue and other income	169.3	147.6	106.0
Benefits and expenses:
Commissions and other operating expenses	145.6	128.2	89.3
Total insurance product margin	23.7	19.4	16.7
Expenses not allocated to product lines
Revenues:
Fee revenue and other income	30.5	17.2	6.9
Benefits and expenses:
Expenses not allocated to product lines	71.3	95.4	90.7
Total insurance product margin	(40.8)	(80.5)	(83.8)
Annuity | Insurance Product Lines
Revenues:
Insurance policy income	23.1	19.6	18.8
Net investment income	466.8	462.4	465.1
Total insurance product line revenue	489.9	482.0	483.9
Benefits and expenses:
Insurance policy benefits	124.3	(14.5)	(93.7)
Interest credited	178.1	149.1	170.6
Amortization, non-deferred commissions and advertising expense	26.4	77.1	110.3
Total expenses	328.8	211.7	187.2
Total insurance product margin	161.1	270.3	296.7
Health: | Insurance Product Lines
Revenues:
Insurance policy income	1,617.3	1,661.5	1,699.5
Net investment income	287.6	287.7	282.3
Total insurance product line revenue	1,904.9	1,949.2	1,981.8
Benefits and expenses:
Insurance policy benefits	1,241.0	1,266.3	1,329.7
Amortization, non-deferred commissions and advertising expense	186.6	189.9	192.3
Total expenses	1,427.6	1,456.2	1,522.0
Total insurance product margin	477.3	493.0	459.8
Life: | Insurance Product Lines
Revenues:
Insurance policy income	859.4	842.3	793.0
Net investment income	146.2	144.7	139.6
Total insurance product line revenue	1,005.6	987.0	932.6
Benefits and expenses:
Insurance policy benefits	585.2	613.5	570.0
Interest credited	47.4	44.4	44.5
Amortization, non-deferred commissions and advertising expense	200.1	178.7	153.1
Total expenses	832.7	836.6	767.6
Total insurance product margin	172.9	150.4	165.0
Allocated expenses | Insurance Product Lines
Benefits and expenses:
Total insurance product margin	$ (596.6)	$ (566.5)	$ (557.7)