Balance Sheet Amounts Associated With Medicare Part D (Detail) (USD $) In Millions, unless otherwise specified							1 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Risk Corridor Settlement	Dec. 31, 2013 Risk Corridor Settlement	Sep. 30, 2014 CMS Subsidies/ Discounts	Dec. 31, 2013 CMS Subsidies/ Discounts	Oct. 31, 2014 Subsequent Event Risk Corridor Settlement	Oct. 31, 2014 Subsequent Event CMS Subsidies/ Discounts
Segment Reporting Information [Line Items]
Payable settled							$ 35
Receivable settled								691
Other current assets	3,839	2,122	205	45	1,517	743
Trade accounts payable and accrued expenses	(2,068)	(1,821)	(80)	(71)	(43)	(30)
Net current asset (liability)			$ 125	$ (26)	$ 1,474	$ 713