Balance Sheet Amounts Associated With Medicare Part D (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Other current assets	$ 2,854	$ 2,122
Trade accounts payable and accrued expenses	(2,559)	(1,821)
Other long-term assets	2,155	1,774
Other long-term liabilities	(360)	(289)
Risk Corridor Settlements - Medicare Part D
Segment Reporting Information [Line Items]
Other current assets	50	45
Trade accounts payable and accrued expenses	(51)	(71)
Net current (liability) asset	(1)	(26)
Other long-term assets	184
Other long-term liabilities	(30)
Net long-term asset	154
Total net asset (liability)	153	(26)
CMS Subsidies/Discounts
Segment Reporting Information [Line Items]
Other current assets	1,034	743
Trade accounts payable and accrued expenses	(199)	(30)
Net current (liability) asset	835	713
Total net asset (liability)	$ 835	$ 713