Regulatory Matters - GAS FERC Regulatory Matters (Details) - Pipelines - Southern Company Gas $ in Millions |
12 Months Ended | |
|---|---|---|
|
Dec. 31, 2018
USD ($)
pipeline
|
Oct. 31, 2017
USD ($)
|
|
| Schedule of Regulatory Assets and Liabilities [Line Items] | ||
| Number of gas construction projects | pipeline | 2 | |
| Percentage of construction costs responsible to pay | 5.00% | |
| Investment | $ 83 | |
| Minimum | ||
| Schedule of Regulatory Assets and Liabilities [Line Items] | ||
| Estimated project costs | 7,000 | $ 6,000 |
| Maximum | ||
| Schedule of Regulatory Assets and Liabilities [Line Items] | ||
| Estimated project costs | $ 7,800 | $ 6,500 |