Interest Expense (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Interest Expense [Abstract]
Interest expense before capitalization	$ 379	$ 361	$ 342
Capitalized interest	(22)	(31)	(26)
Interest Expense	357	330	316
Interest Paid, Net	336	309	301
Interest Costs Incurred, Capitalized, Prior Period Reclassification Adjustment	$ 13