Available-For-Sale Securities (Amount Of Available-For-Sale Debt Securities By Maturity Periods) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014
Rabbi Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Less than one year	$ 2
Available-for-sale debt securities, 1-5 years	64
Available-for-sale debt securities, 6-10 years	28
Available-for-sale debt securities, 11-15 years	8
Available-for-sale debt securities, 16-20 years	5
Available-for-sale debt securities, Over 20 years	57
Total Available-for-Sale Debt Securities	164
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	19
Available-for-sale debt securities, 1-5 years	224
Available-for-sale debt securities, 6-10 years	200
Available-for-sale debt securities, 11-15 years	60
Available-for-sale debt securities, 16-20 years	42
Available-for-sale debt securities, Over 20 years	231
Total Available-for-Sale Debt Securities	$ 776