Segment Disclosures (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues from external customers:
Revenues from external customers - United States	$ 7,335	$ 7,728	$ 6,471
Revenues from external customers - Other	151	202	167
Total revenues	7,486	7,930	6,638
Long-lived assets:
Long-lived assets	17,820	12,624	11,792
Total foreign long-lived assets	880	583	408
Total domestic long-lived assets	$ 16,940	$ 12,041	$ 11,384