BENEFITS PAYABLE - Favorable Medical Claims Reserve Development (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Liability for Claims and Claims Adjustment Expense [Line Items]
(Favorable) unfavorable medical claims reserve development	$ (825)	$ (313)	$ (336)
Retail
Liability for Claims and Claims Adjustment Expense [Line Items]
(Favorable) unfavorable medical claims reserve development	(729)	(266)	(386)
Group and Specialty
Liability for Claims and Claims Adjustment Expense [Line Items]
(Favorable) unfavorable medical claims reserve development	(96)	(47)	50
Operating Segments | Retail
Liability for Claims and Claims Adjustment Expense [Line Items]
(Favorable) unfavorable medical claims reserve development	(729)	(266)	(386)
Operating Segments | Group and Specialty
Liability for Claims and Claims Adjustment Expense [Line Items]
(Favorable) unfavorable medical claims reserve development	$ (96)	$ (47)	$ 50