Regulatory Assets, Liabilities, And Balancing Accounts (Long-Term Regulatory Assets) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 6,565	$ 6,506
Pension Benefits [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	2,939	2,899
Deferred Income Taxes [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	1,483	1,444
Utility Retained Generation [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	598	613
Environmental Compliance Costs [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	535	520
Price Risk Management [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	354	339
Electromechanical Meters [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	234	247
Unamortized Loss, Net Of Gain, On Reacquired Debt [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	157	163
Other Long-Term Regulatory Assets [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 265	$ 281