Discontinued Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Summarized results of discontinued operations:
Total operating revenues	$ 0	$ 82	$ 0	$ 182
Total operating expenses	30	(118)	29	(245)
Asset impairment and other charges	0	(11)	0	(22)
Other income	0	2	1	2
Loss before income taxes	30	(45)	30	(83)
Provision (benefit) for income taxes	(12)	16	(13)	30
Loss from operations of discontinued operations	18	(29)	17	(53)
Major components of asset and liabilities of discontinued operations:
Cash and cash equivalents	0	52	0	52	2	79
Other current assets	0		0		7
Carrying value adjustment	0		0		(9)
Assets of discontinued operations	$ 0		$ 0		$ 0