SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Oct. 31, 2025	Oct. 31, 2024
Significant Accounting Policies [Line Items]
Impairment charges		$ 253,000,000	$ 200,000,000	$ 91,000,000
Impairment of indefinite-lived intangible assets		$ 128,000,000	200,000,000	55,000,000
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
Balance of pharmaceutical rebates	$ 1,700,000,000	$ 1,900,000,000	1,700,000,000
Uncommitted receivables purchase facility, total capacity					$ 1,090,000,000.00	$ 1,190,000,000
Uncommitted receivables purchase facility, total capacity, initial term (in years)					1 year	1 year
Uncommitted receivables purchase facility, receivables sold	639,000,000	1,500,000,000	639,000,000
Uncommitted receivables purchase facility, amount collected from manufacturers	168,000,000	1,000,000,000.0
Uncommitted receivables purchase facility, amount collected but not remitted			123,000,000
Uncommitted receivables purchase facility, amount remitted		123,000,000
Uncommitted receivables purchase facility, amount collected and remitted		$ 471,000,000
Typical term of short-duration employer-group prepaid health services policies (in years)		1 year
Goodwill	9,631,000,000	$ 9,686,000,000	9,631,000,000	9,550,000,000
Goodwill impairment loss		0	0	0
Certificates of need
Significant Accounting Policies [Line Items]
Indefinite-lived intangible assets	910,000,000	$ 790,000,000	910,000,000
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	$ 367,000,000	360,000,000
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]
Impairment charge		$ 449,000,000	281,000,000	436,000,000
Severance costs		329,000,000	25,000,000	199,000,000
Assets impairments		$ 40,000,000	$ 256,000,000	237,000,000
Exit From Employer Group Commercial Medical Products Business
Significant Accounting Policies [Line Items]
Severance costs				$ 70,000,000