BENEFITS PAYABLE - Narrative (Details) claim in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) claim	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Claims Development [Line Items]
Favorable medical claims reserve development related to prior fiscal years | $	$ 825	$ 313	$ 336
Retail
Claims Development [Line Items]
Total IBNR | $	5,200
Group and Specialty
Claims Development [Line Items]
Total IBNR | $	$ 532
2021 Claims Incurred Year | Retail
Claims Development [Line Items]
Cumulative number of reported claims	156.1
2021 Claims Incurred Year | Group and Specialty
Claims Development [Line Items]
Cumulative number of reported claims	8.3
2020 Claims Incurred Year | Retail
Claims Development [Line Items]
Cumulative number of reported claims	140.4
2020 Claims Incurred Year | Group and Specialty
Claims Development [Line Items]
Cumulative number of reported claims	9.1
2019 Claims Incurred Year | Retail
Claims Development [Line Items]
Cumulative number of reported claims	129.1
2019 Claims Incurred Year | Group and Specialty
Claims Development [Line Items]
Cumulative number of reported claims	10.1