Regulatory Assets, Liabilities, And Balancing Accounts (Long-Term Regulatory Assets) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 8,311	$ 7,951
Pension Benefits [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	2,467	2,429
Deferred Income Taxes [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	4,195	3,859
Utility Retained Generation [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	342	364
Environmental Compliance Costs [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	770	778
Price Risk Management [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	84	92
Unamortized Loss, Net Of Gain, On Reacquired Debt [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	69	76
Other Long Term Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 384	$ 353