Available-For-Sale Securities (Amount Of Available-For-Sale Debt Securities By Maturity Periods) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 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	51
Available-for-sale debt securities, 6-10 years	28
Available-for-sale debt securities, 11-15 years	7
Available-for-sale debt securities, 16-20 years	7
Available-for-sale debt securities, Over 20 years	72
Total Available-for-Sale Debt Securities	165
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	20
Available-for-sale debt securities, 1-5 years	239
Available-for-sale debt securities, 6-10 years	217
Available-for-sale debt securities, 11-15 years	62
Available-for-sale debt securities, 16-20 years	42
Available-for-sale debt securities, Over 20 years	246
Total Available-for-Sale Debt Securities	$ 826