MEDICARE PART D (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Other current assets	$ 3,884	$ 3,438
Trade accounts payable and accrued expenses	(4,693)	(2,467)
Other long-term assets	2,192	2,226
Other long-term liabilities	(417)	(263)
Risk Corridor Settlement
Segment Reporting Information [Line Items]
Other current assets	9	8
Trade accounts payable and accrued expenses	(130)	(158)
Net current (liability) asset	(121)	(150)
Other long-term assets	29	0
Other long-term liabilities	(110)	0
Net long-term asset	(81)	0
Total net (liability) asset	(202)	(150)
CMS Subsidies/ Discounts
Segment Reporting Information [Line Items]
Other current assets	1,003	1,001
Trade accounts payable and accrued expenses	(2,201)	(128)
Net current (liability) asset	(1,198)	873
Other long-term assets	0	0
Other long-term liabilities	0	0
Net long-term asset	0	0
Total net (liability) asset	$ (1,198)	$ 873