Introduction - Restricted Cash (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 2,931	$ 1,396
Cash and cash equivalents held for sale		9
Restricted cash:
Total cash, cash equivalents, and restricted cash	2,935	1,519	$ 1,891	$ 2,147
Restricted cash
Restricted cash:
Restricted cash		0
Other accounts and notes receivable
Restricted cash:
Restricted cash	3	114
GEORGIA POWER CO
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	449	4
Cash and cash equivalents held for sale		0
Restricted cash:
Total cash, cash equivalents, and restricted cash	449	112	380	852
GEORGIA POWER CO | Restricted cash
Restricted cash:
Restricted cash		108
GEORGIA POWER CO | Other accounts and notes receivable
Restricted cash:
Restricted cash		0
SOUTHERN Co GAS
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	59	64
Cash and cash equivalents held for sale		0
Restricted cash:
Total cash, cash equivalents, and restricted cash	62	70	$ 62	$ 78
SOUTHERN Co GAS | Restricted cash
Restricted cash:
Restricted cash		0
SOUTHERN Co GAS | Other accounts and notes receivable
Restricted cash:
Restricted cash	$ 3	$ 6