INCOME TAXES - NOL Carryforwards (Details) $ in Millions	Dec. 31, 2025 USD ($)
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	$ 250
Operating loss carryforwards, valuation allowance	(85)
Mississippi Power | Mississippi
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	167
Operating loss carryforwards, valuation allowance	(32)
Southern Power
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	37
Operating loss carryforwards, valuation allowance	(23)
Southern Power | Oklahoma
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	25
Operating loss carryforwards, valuation allowance	(13)
Southern Power | Florida
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	10
Operating loss carryforwards, valuation allowance	(10)
Southern Power | Other states
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	2
Operating loss carryforwards, valuation allowance	0
Other Subsidiaries | Other states
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	21
Operating loss carryforwards, valuation allowance	(5)
Other Subsidiaries | New York
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	11
Operating loss carryforwards, valuation allowance	(11)
Other Subsidiaries | New York City
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	14
Operating loss carryforwards, valuation allowance	$ (14)