Supplementary Financial Information (Other Income and Deductions) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Finite-Lived Intangible Assets [Line Items]
Land Sales	$ 0	$ 2	$ 6	$ 2
Mineral rights royalty income	1	1	3	3
Favorable Counterparty Contract Settlement	2	0	2	0
All other	1	2	4	6
Total other income	4	5	15	11
All other	2	5	4	8
Total other deductions	25	5	86	8
Favorable purchase and sales contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Impairment of Intangible Assets (Excluding Goodwill)	0	0	8	0
Environmental allowances and credits [Member]
Finite-Lived Intangible Assets [Line Items]
Impairment of Intangible Assets (Excluding Goodwill)	4	0	55	0
Mine Development [Member]
Finite-Lived Intangible Assets [Line Items]
Impairment of Intangible Assets (Excluding Goodwill)	$ 19	$ 0	$ 19	$ 0