Available-For-Sale Securities (Amount Of Available-For-Sale Debt Securities By Maturity Periods) (Detail) $ in Millions	Jun. 30, 2015 USD ($)
Rabbi Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	$ 1
1 - 5 years	56
6 - 10 years	37
11 - 15 years	9
16 - 20 years	8
Over 20 years	79
Total Available-for-Sale Debt Securities	190
Power [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	9
1 - 5 years	229
6 - 10 years	197
11 - 15 years	53
16 - 20 years	47
Over 20 years	306
Total Available-for-Sale Debt Securities	$ 841