Regulatory Assets and Liabilities - Summary of Composition of Regulatory Liabilities (Details) - USD ($) $ in Millions |
Dec. 31, 2019 |
Dec. 31, 2018 |
|---|---|---|
| Regulatory Liabilities [Line Items] | ||
| Regulatory liability | $ 1,806 | $ 1,907 |
| Income taxes recovered through rates | ||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liability | 1,258 | 1,279 |
| Removal costs recovered through rates | ||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liability | 297 | 309 |
| Postretirement benefit liability | ||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liability | 186 | 209 |
| Other | ||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liability | 102 | 110 |
| Assets held for sale | ||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liability | $ 37 | $ 0 |