Balance Sheet Amounts Associated With Medicare Part D (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Other current assets	$ 2,605	$ 2,122
Trade accounts payable and accrued expenses	(2,752)	(1,821)
Other long-term assets	1,848	1,774
Other long-term liabilities	(330)	(289)
Risk Corridor Settlements - Medicare Part D
Segment Reporting Information [Line Items]
Other current assets	44	45
Trade accounts payable and accrued expenses	(45)	(71)
Net current (liability) asset	(1)	(26)
Other long-term assets	68	0
Other long-term liabilities	(31)	0
Net long-term asset	37	0
Total net asset (liability)	36	(26)
CMS Subsidies/Discounts
Segment Reporting Information [Line Items]
Other current assets	880	743
Trade accounts payable and accrued expenses	(406)	(30)
Net current (liability) asset	474	713
Other long-term assets	0	0
Other long-term liabilities	0	0
Net long-term asset	0	0
Total net asset (liability)	$ 474	$ 713