Income Taxes - Amortization of Deferred Credits (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Income Tax Disclosure [Line Items] | |||
| Amortization of deferred investment tax credits | $ 87 | $ 79 | $ 59 |
| Southern Power | |||
| Income Tax Disclosure [Line Items] | |||
| Amortization of deferred investment tax credits | $ 58 | $ 57 | $ 37 |