BASIS OF PRESENTATION - Cash and Cash Equivalents (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Cash and Cash Equivalents
Cash and cash equivalents	$ 3,514		$ 262
Accrued property and equipment purchases for items received but not yet paid	45		136
Non-cancellable finance leases entered into	43	$ 58
Non-cancellable operating leases liability entered into	88	$ 139
Captive insurance subsidiaries
Cash and Cash Equivalents
Cash and cash equivalents	176		176
Health plan-related businesses
Cash and Cash Equivalents
Cash and cash equivalents	1		2
Accounts payable
Cash and Cash Equivalents
Book overdrafts classified as accounts payable	160		246
Accrued property and equipment purchases for items received but not yet paid	$ 32		$ 119