NET OPERATING REVENUES - Net Operating Revenue Composition, Ambulatory Segment (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Net operating revenues	$ 4,915	$ 4,557	$ 3,648	$ 4,520	$ 4,806	$ 4,568	$ 4,560	$ 4,545	$ 17,640	$ 18,479	$ 18,313
Ambulatory Care
Disaggregation of Revenue [Line Items]
Net operating revenues									2,072	2,158	2,085
Net patient service revenues | Ambulatory Care
Disaggregation of Revenue [Line Items]
Net operating revenues									1,960	2,040	1,965
Management fees | Ambulatory Care
Disaggregation of Revenue [Line Items]
Net operating revenues									86	95	92
Revenue from other sources | Ambulatory Care
Disaggregation of Revenue [Line Items]
Net operating revenues									$ 26	$ 23	$ 28