Available-For-Sale Securities (Amount Of Available-For-Sale Debt Securities By Maturity Periods) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Rabbi Trust [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	60
Available-for-sale debt securities, 6-10 years	27
Available-for-sale debt securities, 11-15 years	9
Available-for-sale debt securities, 16-20 years	4
Available-for-sale debt securities, Over 20 years	55
Total Available-for-Sale Debt Securities	155
Power [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Less than one year	38
Available-for-sale debt securities, 1-5 years	216
Available-for-sale debt securities, 6-10 years	184
Available-for-sale debt securities, 11-15 years	54
Available-for-sale debt securities, 16-20 years	29
Available-for-sale debt securities, Over 20 years	254
Total Available-for-Sale Debt Securities	$ 775