Introduction - Schedule of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 1,582	$ 1,065
Cash and cash equivalents classified as held for sale	8	0
Restricted cash:
Total cash, cash equivalents, and restricted cash	1,617	1,068	$ 1,885	$ 1,978
Other current assets
Restricted cash:
Restricted cash	2	2
Other deferred charges and assets
Restricted cash:
Restricted cash	24	0
SOUTHERN POWER CO
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	165	182
Cash and cash equivalents classified as held for sale	0
Restricted cash:
Total cash, cash equivalents, and restricted cash	189	183	156	279
SOUTHERN POWER CO | Other current assets
Restricted cash:
Restricted cash	0
SOUTHERN POWER CO | Other deferred charges and assets
Restricted cash:
Restricted cash	24
SOUTHERN Co GAS
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	37	17
Cash and cash equivalents classified as held for sale	8	0
Restricted cash:
Total cash, cash equivalents, and restricted cash	48	19	$ 124	$ 49
SOUTHERN Co GAS | Other current assets
Restricted cash:
Restricted cash	2	2
SOUTHERN Co GAS | Other deferred charges and assets
Restricted cash:
Restricted cash	$ 0	$ 0