INTRODUCTION - Restricted Cash (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 1,879	$ 1,975
Restricted cash:
Total cash, cash equivalents, and restricted cash	1,885	1,978	$ 1,386	$ 1,519
Other accounts and notes receivable
Restricted cash:
Restricted cash	0	3
Other current assets
Restricted cash:
Restricted cash	4	0
Other deferred charges and assets
Restricted cash:
Restricted cash	2	0
SOUTHERN POWER CO
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	154	279
Restricted cash:
Total cash, cash equivalents, and restricted cash	156	279	370	181
SOUTHERN POWER CO \| Other accounts and notes receivable
Restricted cash:
Restricted cash	0
SOUTHERN POWER CO \| Other current assets
Restricted cash:
Restricted cash	0
SOUTHERN POWER CO \| Other deferred charges and assets
Restricted cash:
Restricted cash	2
SOUTHERN Co GAS
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	120	46
Restricted cash:
Total cash, cash equivalents, and restricted cash	124	49	$ 60	$ 70
SOUTHERN Co GAS \| Other accounts and notes receivable
Restricted cash:
Restricted cash	0	3
SOUTHERN Co GAS \| Other current assets
Restricted cash:
Restricted cash	4	0
SOUTHERN Co GAS \| Other deferred charges and assets
Restricted cash:
Restricted cash	$ 0	$ 0