CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($) investor	Dec. 31, 2019 USD ($)
Schedule of Equity Method Investments [Line Items]
Assets	$ 123,158	$ 118,700
Liabilities	90,367	86,650
Equity method investments	403	391
SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	13,424	14,300
Liabilities	6,813	7,678
Equity method investments	$ 19	28
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	$ 6,300	6,400
Liabilities	382	382
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	129	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	$ 1,100
Liabilities	109	104
Noncontrolling interests related to other partners' interests	$ 471	$ 409