Summary of Significant Accounting Policies (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Accounts Receivable (Numeric) [Abstract]
Purchases of accounts receivable	$ 219	$ 203	$ 671	$ 428