Supplemental Financial Information - Accounts Receivable (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Accounts Receivable, Net, Current [Abstract]
Accounts receivable	$ 1,141	$ 1,048
Less: allowance for doubtful accounts	(17)	(16)
Total accounts receivable, net	1,124	1,032
Trade [Member]
Accounts Receivable, Net, Current [Abstract]
Accounts receivable	1,087	1,002
Other [Member]
Accounts Receivable, Net, Current [Abstract]
Accounts receivable	$ 54	$ 46