SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	1 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) employee	Dec. 31, 2018 USD ($)	Oct. 31, 2020	Nov. 02, 2017 USD ($)
Significant Accounting Policies [Line Items]
Hospital utilization as a percentage of historic baseline levels					95.00%
Non-COVID utilization below normal levels		15.00%
Associates impacted by workforce reduction program | employee			1,000
Workforce reduction program charges			$ 47,000,000
Workforce optimization obligation			45,000,000
Consumer discounts on brand name prescription drugs		50.00%
Pharmaceutical rebates		$ 1,400,000,000	1,300,000,000
Typical term (in years) of short-duration employer-group prepaid health services policies		1 year
Number of days notice for employer group to cancel short-duration prepaid health services policies		30 days
Goodwill		$ 4,447,000,000	3,928,000,000	$ 3,897,000,000
Goodwill impairment loss		0	0	0
Clinical reporting unit
Significant Accounting Policies [Line Items]
Goodwill		524,000,000
Provider reporting unit
Significant Accounting Policies [Line Items]
Goodwill		$ 761,000,000
Equipment | Minimum
Significant Accounting Policies [Line Items]
Long-lived assets estimated useful life (in years)		3 years
Equipment | Maximum
Significant Accounting Policies [Line Items]
Long-lived assets estimated useful life (in years)		10 years
Computer software | Minimum
Significant Accounting Policies [Line Items]
Long-lived assets estimated useful life (in years)		3 years
Computer software | Maximum
Significant Accounting Policies [Line Items]
Long-lived assets estimated useful life (in years)		5 years
Building | Minimum
Significant Accounting Policies [Line Items]
Long-lived assets estimated useful life (in years)		10 years
Building | Maximum
Significant Accounting Policies [Line Items]
Long-lived assets estimated useful life (in years)		20 years
Services
Significant Accounting Policies [Line Items]
Accounts receivable		$ 161,000,000	141,000,000
TRICARE
Significant Accounting Policies [Line Items]
TRICARE health care cost payments		6,300,000,000	6,500,000,000	5,600,000,000
TRICARE health care cost reimbursements		6,300,000,000	6,400,000,000	5,600,000,000
Difference between TRICARE health care costs payments and reimbursements		(1,000,000)	(63,000,000)	38,000,000
CMS reinsurance subsidies and discounts
Significant Accounting Policies [Line Items]
Subsidy and discount payments		13,300,000,000	11,800,000,000	10,300,000,000
Subsidy reimbursements		12,400,000,000	11,200,000,000	9,600,000,000
Subsidy and discount payments in excess of reimbursements		$ 900,000,000	$ 600,000,000	700,000,000
Settlement period after close		9 months
CMS brand name prescription drug discounts | Minimum
Significant Accounting Policies [Line Items]
Settlement period after close		14 months
CMS brand name prescription drug discounts | Maximum
Significant Accounting Policies [Line Items]
Settlement period after close		18 months
US Risk Corridor Premium Stabilization Program
Significant Accounting Policies [Line Items]
Litigation recoveries sought						$ 611,000,000
Payment received upon judgement	$ 609,000,000	$ 609,000,000
Related legal fees and expenses		31,000,000
Health Care Reform
Significant Accounting Policies [Line Items]
Payment of annual health insurance industry fee		$ 1,180,000,000		$ 1,040,000,000.00