CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - Narrative (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($) investor	Dec. 31, 2019 USD ($)
Schedule of Equity Method Investments [Line Items]
Assets	$ 119,731	$ 118,700
Liabilities	87,479	86,650
Equity method investments	379	391
SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	13,557	14,300
Liabilities	6,898	7,678
Equity method investments	19	28
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Assets	21,500	21,687
Liabilities	11,731	12,181
Equity method investments	$ 20	20
SP Solar Holdings I, LP | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage	67.00%
SP Solar Holdings I, LP | Global Atlantic
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage	33.00%
Variable Interest Entity, Primary Beneficiary | SP Solar Holdings I, LP | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	$ 6,200	6,400
Liabilities	381	381
Noncontrolling interests related to other partners' interests	1,100	1,100
Variable Interest Entity, Primary Beneficiary | SP Wind | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	2,400	2,500
Liabilities	125	128
Noncontrolling interests related to other partners' interests	$ 44	45
Distribution made to limited partner, cash distributions paid, percentage	60.00%
Number of financial investors | investor	3
Variable Interest Entity, Primary Beneficiary | SP Wind | Financial Investors
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage	40.00%
Variable Interest Entity, Primary Beneficiary | Other Variable Interest Entities | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	$ 1,500	1,100
Liabilities	160	104
Noncontrolling interests related to other partners' interests	$ 557	$ 409