CONTINGENCIES, COMMITMENTS, AND GUARANTEES - Environmental Remediation (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) state site	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Georgia Power
Environmental Exit Cost [Line Items]
Costs recovered annually	$ 12,000,000	$ 12,000,000	$ 2,000,000
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Environmental remediation liability, current	17,000,000	15,000,000
Accrued environmental remediation	0	0
Under recovered environmental remediation costs, other regulatory assets, current	12,000,000	12,000,000
Under recovered environmental remediation costs, other regulatory assets, deferred	23,000,000	29,000,000
Southern Company Gas
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Environmental remediation liability, current	52,000,000	29,000,000
Accrued environmental remediation	197,000,000	216,000,000
Under recovered environmental remediation costs, other regulatory assets, current	59,000,000	34,000,000
Under recovered environmental remediation costs, other regulatory assets, deferred	$ 208,000,000	236,000,000
Southern Company Gas | Manufactured Gas Plants
Environmental Exit Cost [Line Items]
Number of sites | site	40
Number of states in which subject to environmental remediation liabilities | state	4
Alabama Power
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Environmental remediation liability, current	$ 0	0
Southern Company
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Environmental remediation liability, current	69,000,000	44,000,000
Accrued environmental remediation	197,000,000	216,000,000
Under recovered environmental remediation costs, other regulatory assets, current	71,000,000	46,000,000
Under recovered environmental remediation costs, other regulatory assets, deferred	$ 231,000,000	$ 265,000,000