CONTRACT BALANCES - Ambulatory Care Segment (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Contract liabilities	$ 1,055	$ 659
Contract liabilities – long-term	351	918
Ambulatory Care
Disaggregation of Revenue [Line Items]
Contract liabilities	106	93	$ 167	$ 0
Contract liabilities – long-term	34	83	$ 0	$ 0
Contract liabilities advance payments	11
Equity Method Investment, Nonconsolidated Investee or Group of Investees | Ambulatory Care
Disaggregation of Revenue [Line Items]
Contract liabilities	61	51
Contract liabilities – long-term	31	$ 62
Contract liabilities advance payments	$ 12