Consolidated Entities and Equity Method Investments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 1,365		$ 1,318
Earnings from equity method investments	50	$ 32
Assets	157,031		155,720
Liabilities	117,119		116,853
Southern Holdings Company
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	125		124
Earnings from equity method investments	0	0
SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	0	0
Assets	12,474		12,657
Liabilities	6,080		6,136
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,224		1,182
Earnings from equity method investments	46	39
Assets	27,551		27,387
Liabilities	16,118		16,260
SOUTHERN Co GAS | Other
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	34		34
Earnings from equity method investments	$ 0	$ 0
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 | Financial Investors
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	$ 5,100		5,200
Liabilities	361		360
Noncontrolling interests related to other partners' interests	899		918
Variable Interest Entity, Primary Beneficiary | Other Variable Interest Entities | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	1,600		1,600
Liabilities	246		236
Noncontrolling interests related to other partners' interests	$ 590		$ 617