Medicare Part D Pharmacy Benefits Medicare Part D Pharmacy Benefits (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Other current receivables	$ 3,772	$ 2,889
Other policy liabilities	5,484	4,910
CMS Subsidies [Member]
Other current receivables	638	461
Other policy liabilities	0	0
Drug Discount [Member]
Other current receivables	523	314
Other policy liabilities	380	319
Risk-Share [Member]
Other current receivables	0	0
Other policy liabilities	$ 469	$ 438