Available-For-Sale Securities (Fair Value Of Rabbi Trust) (Detail) - Rabbi Trust [Member] - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Total Rabbi Trust Available-for-Sale Securities	$ 224	$ 217
Power [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Rabbi Trust Available-for-Sale Securities	55	53
PSE And G [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Rabbi Trust Available-for-Sale Securities	45	43
Other Entity [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Rabbi Trust Available-for-Sale Securities	$ 124	$ 121