SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Oct. 31, 2024
Significant Accounting Policies [Line Items]
Impairment of indefinite-lived intangible assets	$ 200,000,000	$ 55,000,000	$ 0
Asset impairment charges		91,000,000	0
Minimum collateral as percentage of fair value of investment securities	102.00%
Health services term (in years)	1 year
Number of days notice for employer group to cancel short-duration prepaid health services policies (in days)	30 days
Consumer discounts on brand name and generic prescription drugs (as percent)	75.00%
Balance of pharmaceutical rebates	$ 1,700,000,000	2,300,000,000
Uncommitted receivables purchase facility, total capacity				$ 1,190,000,000
Uncommitted receivables purchase facility, total capacity, initial term (in years)				1 year
Uncommitted receivables purchase facility, cash proceeds received for assets derecognized	639,000,000
Uncommitted receivables purchase facility, amount collected from manufacturers	168,000,000
Uncommitted receivables purchase facility, amount collected but not remitted	$ 123,000,000
Typical term of short-duration employer-group prepaid health services policies (in years)	1 year
Goodwill	$ 9,631,000,000	9,550,000,000	9,142,000,000
Goodwill impairment loss	0	0	0
Certificates of need
Significant Accounting Policies [Line Items]
Indefinite-lived intangible assets	$ 910,000,000	1,092,000,000
Reinsurance Policy, Type [Axis]: CMS reinsurance subsidies and discounts
Significant Accounting Policies [Line Items]
Settlement period after close (in months)	9 months
Home Solutions Reporting Unit
Significant Accounting Policies [Line Items]
Goodwill	$ 4,400,000,000
Services
Significant Accounting Policies [Line Items]
Accounts receivable	$ 360,000,000	357,000,000
Minimum | Reinsurance Policy, Type [Axis]: CMS brand name prescription drug discounts
Significant Accounting Policies [Line Items]
Settlement period after close (in months)	14 months
Minimum | Equipment
Significant Accounting Policies [Line Items]
Long-lived assets estimated useful life (in years)	3 years
Minimum | Computer Software
Significant Accounting Policies [Line Items]
Long-lived assets estimated useful life (in years)	3 years
Minimum | Building
Significant Accounting Policies [Line Items]
Long-lived assets estimated useful life (in years)	10 years
Maximum | Reinsurance Policy, Type [Axis]: CMS brand name prescription drug discounts
Significant Accounting Policies [Line Items]
Settlement period after close (in months)	18 months
Maximum | Equipment
Significant Accounting Policies [Line Items]
Long-lived assets estimated useful life (in years)	10 years
Maximum | Computer Software
Significant Accounting Policies [Line Items]
Long-lived assets estimated useful life (in years)	5 years
Maximum | Building
Significant Accounting Policies [Line Items]
Long-lived assets estimated useful life (in years)	20 years
Value Creation Initiatives
Significant Accounting Policies [Line Items]
Restructuring and impairment charge	$ 281,000,000	436,000,000	473,000,000
Assets held for abandonment	256,000,000	237,000,000	248,000,000
Severance costs	$ 25,000,000	199,000,000	$ 116,000,000
Exit From Employer Group Commercial Medical Products Business
Significant Accounting Policies [Line Items]
Severance costs		$ 70,000,000