MEDICARE PART D (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Other current assets	$ 5,337	$ 4,712
Trade accounts payable and accrued expenses	(3,873)	(2,212)
Other long-term assets	2,731	2,475
Other long-term liabilities	(347)	(235)
Risk Corridor Settlement
Segment Reporting Information [Line Items]
Other current assets	41	25
Trade accounts payable and accrued expenses	(39)	(47)
Net current (liability) asset	2	(22)
Other long-term assets	54	0
Other long-term liabilities	(40)	0
Net long-term asset	14	0
Total net (liability) asset	16	(22)
CMS Subsidies/ Discounts
Segment Reporting Information [Line Items]
Other current assets	2,370	2,082
Trade accounts payable and accrued expenses	(591)	(63)
Net current (liability) asset	1,779	2,019
Other long-term assets	0	0
Other long-term liabilities	0	0
Net long-term asset	0	0
Total net (liability) asset	$ 1,779	$ 2,019