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 |