Supplemental Balance Sheet Information (Accounts Receivable) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Supplemental Balance Sheet Information [Abstract]
Accounts receivable	$ 963	$ 921
Allowance for doubtful accounts	(1)	(2)
Total accounts receivable, net	$ 962	$ 919	[1]

[1] Amounts as of December 31, 2011 were derived from the December 31, 2011 audited financial statements.