Trust Investments (Schedule Of Accounts Receivable And Accounts Payable) (Detail) - USD ($) $ in Millions |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | ||
| Schedule of Trust Investments [Line Items] | ||
| Accounts Receivable | $ 13 | $ 24 |
| Accounts Payable | 9 | 74 |
| Rabbi Trust [Member] | ||
| Schedule of Trust Investments [Line Items] | ||
| Accounts Receivable | 2 | 2 |
| Accounts Payable | $ 0 | $ 1 |