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FAIR VALUE - Narrative (Details) - USD ($) | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2025 | Dec. 31, 2024 | Jun. 30, 2024 | Jun. 30, 2025 | Jun. 30, 2024 | Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |
Fair value measurement, transfers into or out of level 3 |  |  |  | $ 0 | $ 0 |
Swap asset | $ 68,000,000 |  |  | 68,000,000 |  |
Swap liability | 37,000,000 | $ 129,000,000 |  | 37,000,000 |  | $ 129,000,000
Impairment of indefinite-lived intangible assets | 32,000,000 | 200,000,000 | $ 0 | 32,000,000 | $ 0 |
WCAS, Cohort Of Clinics | Minimum |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |
Call option strike price | 3,000,000,000 | 2,500,000,000 |  | 3,000,000,000 |  | 2,500,000,000
WCAS, Cohort Of Clinics | Maximum |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |
Call option strike price | 5,000,000,000 | 3,500,000,000 |  | 5,000,000,000 |  | 3,500,000,000
Put Option |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |
Fair value of financial liability | 1,250,000,000 | 883,000,000 |  | 1,250,000,000 |  | 883,000,000
Call Option |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |
Fair value of financial asset | 13,000,000 | 10,000,000 |  | 13,000,000 |  | 10,000,000
Commercial Paper |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |
Commercial paper borrowings | 0 | 0 |  | 0 |  | 0
Carrying Value |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |
Debt outstanding | 12,600,000,000 | 11,700,000,000 |  | 12,600,000,000 |  | 11,700,000,000
Fair Value |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |
Debt outstanding | 12,100,000,000 | 11,200,000,000 |  | 12,100,000,000 |  | 11,200,000,000
Interest Rate Swap |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |
Cumulative, aggregate adjustment to the carrying value of senior note | 31,000,000 |  |  | 31,000,000 |  |
Recurring Basis |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |
Assets, fair value | 22,421,000,000 | 21,101,000,000 |  | $ 22,421,000,000 |  | $ 21,101,000,000
Unobservable Inputs (Level 3) | Investments | Fair Value Risk |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |
Concentration risk (as percent) |  |  |  | 1.80% |  | 1.50%
Unobservable Inputs (Level 3) | Recurring Basis |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |
Assets, fair value | $ 394,000,000 | $ 322,000,000 |  | $ 394,000,000 |  | $ 322,000,000

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