Available-For-Sale Securities (Amount Of Available-For-Sale Debt Securities By Maturity Periods) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012
Rabbi Trust Fund [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	29
Available-for-sale debt securities, 11-15 years	16
Available-for-sale debt securities, 16-20 years	5
Available-for-sale debt securities, Over 20 years	52
Total Available-for-Sale Debt Securities	160
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	15
Available-for-sale debt securities, 1-5 years	138
Available-for-sale debt securities, 6-10 years	178
Available-for-sale debt securities, 11-15 years	34
Available-for-sale debt securities, 16-20 years	11
Available-for-sale debt securities, Over 20 years	250
Total Available-for-Sale Debt Securities	$ 626

Amount of debt securities categorized neither as held-to-maturity nor trading.

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