Supplementary Financial Information (Other Noncurrent Liabilities and Deferred Credits) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Supplementary Financial Information [Abstract]
Uncertain tax positions, including accrued interest	$ 54		$ 54		$ 74
Asset retirement and mining reclamation obligations	671		671		560
Unfavorable purchase and sales contracts	549		549		566
Nuclear decommissioning fund excess over asset retirement obligation (Note 14)	372		372		479
Other, including retirement and other employee benefits	21		21		20
Total other noncurrent liabilities and deferred credits	1,667		1,667		$ 1,699
Amortization of Deferred Charges
Amortization of Unfavorable Purchase and Sales Contracts	$ 6	$ 6	17	$ 17
Future Amortization Expense
2015			24
2016			24
2017			24
2018			24
2019			$ 24