Trust Investments (Narrative) (Detail)
$ in Millions |
3 Months Ended |
|
Mar. 31, 2018
USD ($)
Facility
|
|---|
| Power [Member] |
|
| Schedule of Trust Investments [Line Items] |
|
| Number of Nuclear Facilities | Facility |
5
|
| Total Debt Securities [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] |
|
| Schedule of Trust Investments [Line Items] |
|
| After tax amount of net unrealized gains recognized in AOCI |
$ (10)
|
| Equity Securities [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] |
|
| Schedule of Trust Investments [Line Items] |
|
| Unrealized Gains (Losses) on Equity Securities still held |
(10)
|
| Equity Securities [Member] | Rabbi Trust [Member] |
|
| Schedule of Trust Investments [Line Items] |
|
| Unrealized Gains (Losses) on Equity Securities still held |
$ (1)
|