Property, Plant, and Equipment - Assets Subject to Lien (Narrative) (Details) - USD ($) $ in Millions |
Dec. 31, 2018 |
Oct. 02, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|---|---|
| Property, Plant and Equipment [Line Items] | ||||
| Assets, primarily related to property, plant, and equipment, subject to lien | $ 116,914 | $ 111,005 | $ 109,697 | |
| Mississippi Power | ||||
| Property, Plant and Equipment [Line Items] | ||||
| Assets, primarily related to property, plant, and equipment, subject to lien | 4,886 | 4,866 | ||
| Mississippi Power | Chevron | ||||
| Property, Plant and Equipment [Line Items] | ||||
| Net book value of co-generation assets | $ 101 | |||
| Southern Power | ||||
| Property, Plant and Equipment [Line Items] | ||||
| Assets, primarily related to property, plant, and equipment, subject to lien | 14,883 | $ 15,206 | ||
| Southern Power | Senior Lien | ||||
| Property, Plant and Equipment [Line Items] | ||||
| Assets, primarily related to property, plant, and equipment, subject to lien | $ 563 |