Available-For-Sale Securities (Amount Of Available-For-Sale Debt Securities By Maturity Periods) (Detail) $ in Millions	Sep. 30, 2015 USD ($)
Rabbi Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	$ 5
1 - 5 years	49
6 - 10 years	39
11 - 15 years	8
16 - 20 years	9
Over 20 years	80
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	8
1 - 5 years	236
6 - 10 years	201
11 - 15 years	51
16 - 20 years	51
Over 20 years	308
Total Available-for-Sale Debt Securities	$ 855