MEDICARE PART D (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Other current assets	$ 4,487	$ 3,564
Trade accounts payable and accrued expenses	(3,832)	(3,067)
Other long-term assets	1,568	1,375
Other long-term liabilities	(911)	(581)
Risk Corridor Settlement
Segment Reporting Information [Line Items]
Other current assets	11	15
Trade accounts payable and accrued expenses	(48)	(103)
Net current liability	(37)	(88)
Other long-term assets	26	7
Other long-term liabilities	(137)	(89)
Net long-term liability	(111)	(82)
Total net liability	(148)	(170)
CMS Subsidies/ Discounts
Segment Reporting Information [Line Items]
Other current assets	388	172
Trade accounts payable and accrued expenses	(1,259)	(503)
Net current liability	(871)	(331)
Other long-term assets	0	0
Other long-term liabilities	0	0
Net long-term liability	0	0
Total net liability	$ (871)	$ (331)