MEDICARE PART D - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule Of Balance Sheet Components [Line Items]
Trade accounts payable and accrued expenses	$ 1,962	$ 1,783
Other current assets	1,615	1,027
Risk Corridor Settlements
Schedule Of Balance Sheet Components [Line Items]
Trade accounts payable and accrued expenses	428	331
Other current assets	38	2
Risk Corridor Settlements | Expected to be settled in the fourth quarter of 2012
Schedule Of Balance Sheet Components [Line Items]
Trade accounts payable and accrued expenses	289
CMS Subsidies
Schedule Of Balance Sheet Components [Line Items]
Trade accounts payable and accrued expenses	155	139
Other current assets	654	363
CMS Subsidies | Expected to be settled in the fourth quarter of 2012
Schedule Of Balance Sheet Components [Line Items]
Other current assets	$ 376