ACCOUNTS RECEIVABLE - Allowance (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Accounts Receivable Additional Disclosures [Abstract]      
Allowance for doubtful accounts as a percent of patients accounts receivable     26.60%
Accounts receivable and allowance for doubtful accounts      
Estimated costs of caring $ 181 $ 190  
Self-pay patients      
Accounts receivable and allowance for doubtful accounts      
Estimated costs of caring 146 160  
Charity care patients      
Accounts receivable and allowance for doubtful accounts      
Estimated costs of caring 35 30  
Medicaid DSH and other supplemental revenues      
Accounts receivable and allowance for doubtful accounts      
Estimated costs of caring $ 220 $ 158