MEDICARE PART D (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Other current assets	$ 5,384	$ 3,806
Trade accounts payable and accrued expenses	(5,399)	(3,754)
Other long-term assets	2,130	1,834
Other long-term liabilities	(1,186)	(935)
Risk Corridor Settlement
Segment Reporting Information [Line Items]
Other current assets	59	5
Trade accounts payable and accrued expenses	(148)	(120)
Net current (liability) asset	(89)	(115)
Other long-term assets	183	6
Other long-term liabilities	(130)	(61)
Net long-term asset (liability)	53	(55)
Total net (liability) asset	(36)	(170)
CMS Subsidies/ Discounts
Segment Reporting Information [Line Items]
Other current assets	894	585
Trade accounts payable and accrued expenses	(1,241)	(356)
Net current (liability) asset	(347)	229
Other long-term assets	0	0
Other long-term liabilities	0	0
Net long-term asset (liability)	0	0
Total net (liability) asset	$ (347)	$ 229