MEDICARE PART D (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Other current assets	$ 3,776	$ 3,438
Trade accounts payable and accrued expenses	(4,888)	(2,467)
Other long-term assets	2,214	2,226
Other long-term liabilities	(457)	(263)
Risk Corridor Settlement
Segment Reporting Information [Line Items]
Other current assets	9	8
Trade accounts payable and accrued expenses	(118)	(158)
Net current (liability) asset	(109)	(150)
Other long-term assets	3	0
Other long-term liabilities	(180)	0
Net long-term asset (liability)	(177)	0
Total net (liability) asset	(286)	(150)
CMS Subsidies/ Discounts
Segment Reporting Information [Line Items]
Other current assets	1,058	1,001
Trade accounts payable and accrued expenses	(2,134)	(128)
Net current (liability) asset	(1,076)	873
Other long-term assets	0	0
Other long-term liabilities	0	0
Net long-term asset (liability)	0	0
Total net (liability) asset	$ (1,076)	$ 873