Regulatory Assets, Liabilities, And Balancing Accounts (Long-Term Regulatory Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 7,130	$ 7,029
Pension Benefits [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	2,414	2,414
Deferred Income Taxes [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	3,265	3,054
Utility Retained Generation [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	399	411
Environmental Compliance Costs [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	683	748
Price Risk Management [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	134	138
Unamortized Loss, Net Of Gain, On Reacquired Debt [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	90	94
Other Long Term Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 145	$ 170