Significant Accounting Policies - Schedule of Allowance for Funds Used During Construction (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Other Funds | |||
| Significant Accounting Policies [Line Items] | |||
| Allowance for funds used during construction | $ 28 | $ 24 | $ 19 |
| Borrowed Funds | |||
| Significant Accounting Policies [Line Items] | |||
| Allowance for funds used during construction | $ 13 | $ 13 | $ 8 |