BUSINESS SEGMENTS - SCHEDULE OF BALANCE SHEET INFORMATION, BY SEGMENT (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2020
Segment Reporting Information [Line Items]
Total assets	$ 33,339.2	$ 36,204.4	$ 33,613.1
Total liabilities	31,938.4	30,944.7
Investments not allocated to product lines
Segment Reporting Information [Line Items]
Total assets	8,203.0	7,093.0
Total liabilities	5,293.8	4,502.9
Non-life companies included in the fee income segment
Segment Reporting Information [Line Items]
Total assets	207.7	194.0
Total liabilities	23.5	25.0
Other non-life companies
Segment Reporting Information [Line Items]
Total assets	292.9	383.9
Total liabilities	208.8	244.0
Annuity | Insurance Product Lines
Segment Reporting Information [Line Items]
Total assets	11,323.9	13,288.6
Total liabilities	12,367.0	12,283.3
Health: | Insurance Product Lines
Segment Reporting Information [Line Items]
Total assets	9,221.6	10,558.7
Total liabilities	9,727.4	9,610.0
Life insurance inforce: | Insurance Product Lines
Segment Reporting Information [Line Items]
Total assets	4,090.1	4,686.2
Total liabilities	$ 4,317.9	$ 4,279.5