Available-For-Sale Securities (Amount Of Available-For-Sale Debt Securities By Maturity Periods) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Less than one year	$ 44
Available-for-sale debt securities, 1-5 years	180
Available-for-sale debt securities, 6-10 years	180
Available-for-sale debt securities, 11-15 years	45
Available-for-sale debt securities, 16-20 years	26
Available-for-sale debt securities, Over 20 years	245
Total Available-for-Sale Debt Securities	720
Rabbi Trusts [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Less than one year	0
Available-for-sale debt securities, 1-5 years	58
Available-for-sale debt securities, 6-10 years	30
Available-for-sale debt securities, 11-15 years	7
Available-for-sale debt securities, 16-20 years	4
Available-for-sale debt securities, Over 20 years	54
Total Available-for-Sale Debt Securities	$ 153