Consolidated Entities and Equity Method Investments - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) investor	Sep. 30, 2024 USD ($)	Dec. 31, 2024 USD ($)
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 1,303		$ 1,303		$ 1,416
Assets	153,248		153,248		145,180
Liabilities	114,974		114,974		108,506
Earnings from equity method investments	33	$ 31	76	$ 107
Southern Holdings Company
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	116		116		128
Earnings from equity method investments	0	$ 0	(20)	$ 0
SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	13,595		13,595		12,653
Liabilities	7,018		$ 7,018		5,971
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%
SP Wind | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage			60.00%
Number of financial investors | investor			3
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 | SP Solar Holdings I, LP | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	5,300		$ 5,300		5,400
Liabilities	365		365		372
Noncontrolling interests related to other partners' interests	1,000		1,000		1,000
Variable Interest Entity, Primary Beneficiary | SP Wind | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	1,800		1,800		2,000
Liabilities	190		190		177
Noncontrolling interests related to other partners' interests	30		30		35
Variable Interest Entity, Primary Beneficiary | Other Variable Interest Entities | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	1,600		1,600		1,600
Liabilities	241		241		224
Noncontrolling interests related to other partners' interests	$ 642		$ 642		$ 691