Supplementary Financial Information (Other Noncurrent Liabilities and Deferred Credits) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended	3 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Audit Years 1997 Through 2002 [Member]	Sep. 30, 2013 Audit Years 1997 Through 2002 [Member] Internal Revenue Service (IRS) [Member]	Sep. 30, 2013 Audit Years 1997 Through 2002 [Member] State and Local Jurisdiction [Member]	Sep. 30, 2013 Audit Years 1997 Through 2002 [Member] Reclassification out of Accumulated Deferred Income Tax Liability [Member] Internal Revenue Service (IRS) [Member]	Mar. 31, 2013 Audit Years 2003 Through 2006 [Member] Internal Revenue Service (IRS) [Member]	Sep. 30, 2013 Audit Years 2003 Through 2006 [Member] Internal Revenue Service (IRS) [Member]
Other Noncurrent Liabilities Noncurrent and Deferred Credits [Line Items]
Uncertain tax positions (including accrued interest)	$ 384		$ 384		$ 1,250
Asset retirement and mining reclamation obligations	444		444		452
Unfavorable purchase and sales contracts	596		596		620
Nuclear decommissioning cost over-recovery	352		352		284
Other, including retirement and other employee benefits	17		17		37
Total other noncurrent liabilities and deferred credits	1,793		1,793		2,643
Accumulated deferred income taxes	3,347		3,347		3,759				411
Income tax benefit (expense)	(17)	(228)	(476)	(692)			78	14	20
Reduction of non current income tax expense						392
Unrecognized tax benefits, period increase (decrease)										794
Income tax examination, reclassification to accumulated deferred income tax liability										685
Unrecognized tax benefits, decreases resulting from settlements										109
Income tax examination, estimated reversal of Accrued Interest from Examination, Net of Tax										62
Deferred tax liabilities, gross											430
Amortization of Deferred Charges
Amortization of Unfavorable Purchase and Sales Contracts	6		19	20
Future Amortization Expense
2013					25
2014					24
2015					23
2016					23
2017					$ 23