Variable Interest Entities (VIEs) (Detail) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Variable Interest Entity [Line Items] | ||
| Operating Revenues | $ 2,818 | $ 2,591 |
| Operation and Maintenance | 754 | 717 |
| Long Island ServCo [Member] | ||
| Variable Interest Entity [Line Items] | ||
| Operating Revenues | 120 | 112 |
| Operation and Maintenance | $ 120 | $ 112 |