MEDICARE PART D (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Other current assets	$ 3,519	$ 3,564
Trade accounts payable and accrued expenses	(3,640)	(3,067)
Other long-term assets	1,605	1,375
Other long-term liabilities	(897)	(581)
Risk Corridor Settlement
Segment Reporting Information [Line Items]
Other current assets	11	15
Trade accounts payable and accrued expenses	(49)	(103)
Net current liability	(38)	(88)
Other long-term assets	25	7
Other long-term liabilities	(142)	(89)
Net long-term liability	(117)	(82)
Total net liability	(155)	(170)
CMS Subsidies/ Discounts
Segment Reporting Information [Line Items]
Other current assets	337	172
Trade accounts payable and accrued expenses	(781)	(503)
Net current liability	(444)	(331)
Other long-term assets	0	0
Other long-term liabilities	0	0
Net long-term liability	0	0
Total net liability	$ (444)	$ (331)