Interest Expense (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Interest Expense
Interest expense	$ 135	$ 156	$ 399	$ 440
Interest income	(1)	(1)	(2)	(3)
Interest expense, net	$ 134	$ 155	$ 397	$ 437