Consolidated Entities and Equity Method Investments - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021 USD ($) investor	Dec. 31, 2020 USD ($)
Schedule of Equity Method Investments [Line Items]
Assets	$ 127,861	$ 122,935
Liabilities	94,351	90,410
Equity investments in unconsolidated subsidiaries	1,278	1,362
SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	13,611	13,235
Liabilities	6,904	6,604
Equity investments in unconsolidated subsidiaries	$ 83	19
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	6,100
Liabilities	364	387
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	2,300	2,400
Liabilities	157	138
Noncontrolling interests related to other partners' interests	$ 42	43
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	$ 1,900	1,100
Liabilities	263	110
Noncontrolling interests related to other partners' interests	$ 902	$ 454