Balance Sheet Amounts Associated With Medicare Part D (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Other current assets	$ 1,422	$ 1,027
Trade accounts payable and accrued expenses	(2,081)	(1,783)
Other long-term assets	1,233	1,165
Other long-term liabilities	(321)	(267)
Risk Corridor Settlement
Segment Reporting Information [Line Items]
Other current assets	37	2
Trade accounts payable and accrued expenses	(328)	(331)
Net current (liability) asset	(291)	(329)
Other long-term assets	8	0
Other long-term liabilities	(50)	0
Net long-term liability	(42)	0
Total net (liability) asset	(333)	(329)
CMS Subsidies
Segment Reporting Information [Line Items]
Other current assets	437	363
Trade accounts payable and accrued expenses	(428)	(139)
Net current (liability) asset	9	224
Other long-term assets	0	0
Other long-term liabilities	0	0
Net long-term liability	0	0
Total net (liability) asset	$ 9	$ 224