REGULATORY MATTERS - Alabama Power (Details) - ALABAMA POWER CO $ in Millions	3 Months Ended
	Sep. 30, 2020 USD ($)	Aug. 14, 2020 USD ($) MW	Aug. 07, 2020 USD ($)
Public Utilities, General Disclosures [Line Items]
Approved additional generating capacity, purchases (in MWs) | MW		240
Approved additional generating capacity, demand-side management and distributed energy resource programs (in MWs) | MW		200
Additional generating capacity (in MWs) | MW		400
Bill credits			$ 100
Decrease in NDR for damages incurred	$ 44
Natural disaster reserve	51
Minimum natural disaster reserve balance, triggering establishment charge	50
Natural disaster reserve authorized limit	$ 75
Plant Barry Unit 8
Public Utilities, General Disclosures [Line Items]
Approved additional generating capacity, construction (in MWs) | MW		720
Costs incurred, percentage of estimated in-service costs		5.00%
Estimated in-service cost		$ 652