Available-For-Sale Securities (Amount Of Available-For-Sale Debt Securities By Maturity Periods) (Detail) $ in Millions	Jun. 30, 2016 USD ($)
Rabbi Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	$ 8
1 - 5 years	45
6 - 10 years	48
11 - 15 years	6
16 - 20 years	7
Over 20 years	82
Total Available-for-Sale Debt Securities	196
Power [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	19
1 - 5 years	216
6 - 10 years	220
11 - 15 years	54
16 - 20 years	61
Over 20 years	313
Total Available-for-Sale Debt Securities	$ 883