Supplementary Financial Information (Inventories by Major Category and Other Investments) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Inventories by Major Category
Materials and supplies	$ 215	$ 214
Fuel stock	144	215
Natural gas in storage	29	39
Total inventories	388	468
Other Investments
Nuclear plant decommissioning trust	874	893
Assets related to employee benefit plans, including employee savings programs, net of distributions	1	1
Land	36	37
Miscellaneous other	8	10
Total investments	$ 919	$ 941