MEDICARE PART D (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Other current assets	$ 3,849	$ 3,438
Trade accounts payable and accrued expenses	(4,675)	(2,467)
Other long-term assets	2,167	2,226
Other long-term liabilities	(367)	(263)
Risk Corridor Settlement
Segment Reporting Information [Line Items]
Other current assets	8	8
Trade accounts payable and accrued expenses	(126)	(158)
Net current (liability) asset	(118)	(150)
Other long-term assets	12	0
Other long-term liabilities	(74)	0
Net long-term asset	(62)	0
Total net (liability) asset	(180)	(150)
CMS Subsidies/ Discounts
Segment Reporting Information [Line Items]
Other current assets	1,044	1,001
Trade accounts payable and accrued expenses	(1,895)	(128)
Net current (liability) asset	(851)	873
Other long-term assets	0	0
Other long-term liabilities	0	0
Net long-term asset	0	0
Total net (liability) asset	$ (851)	$ 873