Regulatory Assets, Liabilities, And Balancing Accounts (Long-Term Regulatory Assets) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 4,823	$ 4,913
Pension Benefits [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	1,429	1,444
Deferred Income Taxes [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	1,883	1,835
Utility Retained Generation [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	491	503
Environmental Compliance Costs [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	582	628
Price Risk Management [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	96	106
Electromechanical Meters [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	119	135
Unamortized Loss, Net Of Gain, On Reacquired Debt [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	129	135
Other Long Term Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 94	$ 127