Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Amortization expense on other intangible assets	$ 186	$ 62
Common stock, par value per share (in dollars per share)	$ 5	$ 5
Common stock, shares authorized	1,500,000,000	1,500,000,000
SOUTHERN POWER CO
Amortization expense on other intangible assets	$ 47	$ 22
Common stock, par value per share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	1,000,000	1,000,000
Common stock, shares outstanding	1,000	1,000
SOUTHERN POWER CO | 1.50% due 2018
Fixed stated interest rate of debt obligation		1.50%
SOUTHERN POWER CO | 1.95% due 2019
Fixed stated interest rate of debt obligation	1.95%	1.95%
SOUTHERN POWER CO | 2.375% due 2020
Fixed stated interest rate of debt obligation	2.375%	2.375%
SOUTHERN POWER CO | 2.50% due 2021
Fixed stated interest rate of debt obligation	2.50%	2.50%
SOUTHERN POWER CO | 1.00% due 2022
Fixed stated interest rate of debt obligation	1.00%
SOUTHERN POWER CO | Variable rate (1.88% at 12/31/17) due 2018
Fixed stated interest rate of debt obligation	1.88%	1.88%
SOUTHERN POWER CO | Variable rate (2.18% at 12/31/17) due 2020
Fixed stated interest rate of debt obligation	2.18%
SOUTHERN POWER CO | Variable rate (3.75% at 1/1/17) due 2032-2036
Fixed stated interest rate of debt obligation	3.75%	3.75%
SOUTHERN Co GAS
Amortization expense on other intangible assets	$ 120	$ 34
Common stock, par value per share (in dollars per share)	$ 0.01	$ 10,000.00
Common stock, shares authorized	100,000,000	100
Common stock, shares outstanding	100	100
Minimum | SOUTHERN POWER CO | Senior Notes Due Two Thousand Twenty Three Through Two Thousand Forty Six [Member]
Fixed stated interest rate of debt obligation	1.85%
Minimum | SOUTHERN POWER CO | 1.85% to 5.25% due 2023-2046
Fixed stated interest rate of debt obligation		1.85%
Maximum | SOUTHERN POWER CO | 1.85% to 5.25% due 2023-2046
Fixed stated interest rate of debt obligation	5.25%	5.25%
Predecessor | SOUTHERN Co GAS
Amortization expense on other intangible assets		$ 34