Regulatory Assets and Liabilities - Summary of Composition of Regulatory Assets (Details) - USD ($) $ in Millions |
Dec. 31, 2019 |
Dec. 31, 2018 |
|---|---|---|
| Regulatory Assets [Line Items] | ||
| Regulatory assets | $ 1,128 | $ 1,156 |
| Deferred pension expense | ||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 384 | 362 |
| Removal costs recoverable through rates | ||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 305 | 292 |
| Regulatory balancing accounts | ||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 96 | 110 |
| Other | ||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 398 | 392 |
| Assets held for sale | ||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | $ 55 | $ 0 |