Discontinued Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Summarized results of discontinued operations:
Total operating revenues	$ 0	$ 121	$ 0	$ 303
Total operating expenses	0	(138)	29	(385)
Asset impairment and other charges	0	(113)	0	(134)
Other income	(1)	5	0	7
Loss before income taxes	(1)	(125)	29	(209)
Provision (benefit) for income taxes	0	(49)	13	(80)
Loss from operations of discontinued operations	(1)	(76)	16	(129)
Major components of asset and liabilities of discontinued operations:
Cash and cash equivalents	0	55	0	55	2	79
Other current assets	0		0		7
Carrying value adjustment	0		0		(9)
Assets of discontinued operations	$ 0		$ 0		$ 0