POSTRETIREMENT BENEFITS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Shareholders' Equity Charges
Pretax benefit (charge) to shareholders' equity	$ 16.4	$ (59.9)	$ (245.9)
Other Postretirement Benefit Plans, Defined Benefit
Shareholders' Equity Charges
After-tax benefit (charge) to shareholders' equity for other postretirement plans	1.3	(9.6)
Pretax benefit (charge) to shareholders' equity	1.7	$ (12.2)	$ (3.8)
Par outstanding value of non-callable zero coupon bond used to determine the hypothetical yield curve	250.0
Defined Benefit Plan, Expected Future Benefit Payments in Year One	3.0
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	3.0
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	3.0
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	2.0
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	$ 2.0