COMMITMENTS, GUARANTEES AND CONTINGENCIES (Details) beneficiary in Millions, $ in Millions		3 Months Ended	12 Months Ended
	Jan. 01, 2018 beneficiary	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2018 State	Nov. 02, 2017 USD ($)
Loss Contingencies [Line Items]
Percentage of risk score calculated from claims submitted through EDS		25.00%		15.00%
Number of states comprising TRICARE beneficiaries | State				32
Number of TRICARE beneficiaries | beneficiary	6
Litigation recoveries sought | $					$ 611
Forecast
Loss Contingencies [Line Items]
Percentage of risk score calculated from claims submitted through EDS			50.00%
Medicare
Loss Contingencies [Line Items]
Percentage of premiums and services revenue		82.00%
Military services
Loss Contingencies [Line Items]
Percentage of premiums and services revenue		1.00%
Medicaid
Loss Contingencies [Line Items]
Percentage of premiums and services revenue		4.00%
Tricare East Region Contract
Loss Contingencies [Line Items]
Contract term years				5 years