Financial Risk Management Activities (Schedule Providing Credit Risk From Others, Net Of Collateral) (Detail) - Power [Member]
$ in Millions |
3 Months Ended |
|
Mar. 31, 2018
USD ($)
Counterparty
|
|---|
| Derivative [Line Items] |
|
|
| Current Exposure |
$ 340
|
|
| Securities held as Collateral |
12
|
|
| Net exposure |
328
|
|
| Number of Counterparties greater than 10% |
$ 1
|
|
| Number Of Active Counterparties On Credit Risk Derivatives | Counterparty |
142
|
|
| Investment Grade - External Rating [Member] |
|
|
| Derivative [Line Items] |
|
|
| Percentage Of Credit Exposure |
99.00%
|
|
| Investment Grade [Member] |
|
|
| Derivative [Line Items] |
|
|
| Current Exposure |
$ 337
|
|
| Securities held as Collateral |
12
|
|
| Net exposure |
325
|
|
| Number of Counterparties greater than 10% |
1
|
|
| Amount Of Net Credit Exposure Greater Than Ten Percent |
191
|
[1] |
| External Credit Rating, Non Investment Grade [Member] |
|
|
| Derivative [Line Items] |
|
|
| Current Exposure |
3
|
|
| Securities held as Collateral |
0
|
|
| Amount Of Net Credit Exposure Greater Than Ten Percent |
0
|
|
| Non-Investment Grade [Member] |
|
|
| Derivative [Line Items] |
|
|
| Net exposure |
3
|
|
| Number of Counterparties greater than 10% |
0
|
|
| Letter of Credit [Member] |
|
|
| Derivative [Line Items] |
|
|
| Securities held as Collateral |
$ 12
|
|
|
|