ASSET RETIREMENT OBLIGATIONS - Investment Securities in the Funds (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Marketable Securities [Line Items]
Total investment securities in the Funds	$ 2,034	$ 1,719
Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	1,159	919
Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	798	726
Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	77	74
Alabama Power
Marketable Securities [Line Items]
Total investment securities in the Funds	1,021	846
Alabama Power | Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	743	594
Alabama Power | Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	218	201
Alabama Power | Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	60	51
Georgia Power
Marketable Securities [Line Items]
Total investment securities in the Funds	1,013	873
Georgia Power | Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	416	325
Georgia Power | Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	580	525
Georgia Power | Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	$ 17	$ 23