Trust Investments (Fair Value Of Rabbi Trust) (Detail) - Rabbi Trust [Member] - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Schedule of Trust Investments [Line Items]
Total Rabbi Trust Available-for-Sale Securities	$ 225	$ 231
Power [Member]
Schedule of Trust Investments [Line Items]
Total Rabbi Trust Available-for-Sale Securities	56	57
PSE And G [Member]
Schedule of Trust Investments [Line Items]
Total Rabbi Trust Available-for-Sale Securities	45	46
Other Entity [Member]
Schedule of Trust Investments [Line Items]
Total Rabbi Trust Available-for-Sale Securities	$ 124	$ 128