Regulatory Assets, Liabilities, And Balancing Accounts (Long-Term Regulatory Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 8,546	$ 7,951
Current regulatory assets	573	423
Pension Benefits [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	2,487	2,429
Deferred Income Taxes [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	4,373	3,859
Utility Retained Generation [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	331	364
Environmental Compliance Costs [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	779	778
Price Risk Management [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	77	92
Unamortized Loss, Net Of Gain, On Reacquired Debt [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	65	76
Other Long Term Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	434	$ 353
CEMA [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	189
Current regulatory assets	$ 392
Percent Recoverable	100.00%