EQUITY - Changes in Shareholders' Equity - Noncontrolling interests (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Stockholders equity balance $ 616 $ 1,094 $ 539 $ 1,082
Net income 130 (17)    
Noncontrolling Interests        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Stockholders equity balance 681 664 686 $ 665
Net income 31 36    
Noncontrolling Interests | Hospital Operations and other        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Stockholders equity balance 68   64  
Net income 2 6    
Noncontrolling Interests | Ambulatory Care        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Stockholders equity balance 613   $ 622  
Net income $ 29 $ 30