Commitments - Rent Expense (Details) - USD ($) $ in Millions |
6 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|
Dec. 31, 2016 |
Jun. 30, 2016 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Recorded Unconditional Purchase Obligation [Line Items] | |||||
| Operating leases rent expense | $ 192 | $ 176 | $ 169 | ||
| Alabama Power | |||||
| Recorded Unconditional Purchase Obligation [Line Items] | |||||
| Operating leases rent expense | 23 | 25 | 18 | ||
| Georgia Power | |||||
| Recorded Unconditional Purchase Obligation [Line Items] | |||||
| Operating leases rent expense | 34 | 31 | 28 | ||
| Mississippi Power | |||||
| Recorded Unconditional Purchase Obligation [Line Items] | |||||
| Operating leases rent expense | 4 | 3 | 3 | ||
| Southern Power | |||||
| Recorded Unconditional Purchase Obligation [Line Items] | |||||
| Operating leases rent expense | 31 | 29 | $ 22 | ||
| Southern Company Gas | |||||
| Recorded Unconditional Purchase Obligation [Line Items] | |||||
| Operating leases rent expense | $ 8 | $ 15 | $ 15 | ||
| Predecessor | Southern Company Gas | |||||
| Recorded Unconditional Purchase Obligation [Line Items] | |||||
| Operating leases rent expense | $ 6 | ||||