BENEFITS PAYABLE - Narrative (Details) claim in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) claim	Dec. 31, 2018 USD ($) claim	Dec. 31, 2017 USD ($) claim
Claims Development [Line Items]
Favorable medical claims reserve development related to prior fiscal years | $	$ 336	$ 503	$ 483
Benefit expense reduction excluded from previous short duration benefits payable rollforward | $			$ (22)
Retail
Claims Development [Line Items]
Total IBNR | $	3,600
Group and Specialty
Claims Development [Line Items]
Total IBNR | $	$ 567
2019 Claims Incurred Year | Retail
Claims Development [Line Items]
Cumulative number of reported claims	123.0
2019 Claims Incurred Year | Group and Specialty
Claims Development [Line Items]
Cumulative number of reported claims	9.7
2018 Claims Incurred Year | Retail
Claims Development [Line Items]
Cumulative number of reported claims		109.6
2018 Claims Incurred Year | Group and Specialty
Claims Development [Line Items]
Cumulative number of reported claims		10.8
2017 Claims Incurred Year | Retail
Claims Development [Line Items]
Cumulative number of reported claims			104.7
2017 Claims Incurred Year | Group and Specialty
Claims Development [Line Items]
Cumulative number of reported claims			11.1