Asset Retirement Obligations - Investment Securities in the Funds (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Marketable Securities [Line Items]
Total investment securities in the Funds	$ 1,719	$ 1,831
Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	919	1,059
Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	726	725
Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	74	47
Alabama Power
Marketable Securities [Line Items]
Total investment securities in the Funds	846	902
Alabama Power | Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	594	644
Alabama Power | Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	201	223
Alabama Power | Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	51	35
Georgia Power
Marketable Securities [Line Items]
Total investment securities in the Funds	873	929
Georgia Power | Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	325	415
Georgia Power | Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	525	502
Georgia Power | Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	$ 23	$ 12