LEASES - Lease Costs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Lease cost
Operating lease cost	$ 310
Finance lease cost:
Amortization of ROU assets	28
Interest on lease obligations	12
Total finance lease cost	40
Short-term lease costs	48
Variable lease cost	105
Sublease income	0
Total lease cost	503
Alabama Power
Lease cost
Operating lease cost	54
Finance lease cost:
Amortization of ROU assets	1
Interest on lease obligations	0
Total finance lease cost	1
Short-term lease costs	19
Variable lease cost	6
Sublease income	(1)
Total lease cost	79
Georgia Power
Lease cost
Operating lease cost	206
Finance lease cost:
Amortization of ROU assets	15
Interest on lease obligations	18
Total finance lease cost	33
Short-term lease costs	22
Variable lease cost	85
Sublease income	0
Total lease cost	346
Mississippi Power
Lease cost
Operating lease cost	3
Finance lease cost:
Amortization of ROU assets	0
Interest on lease obligations	0
Total finance lease cost	0
Short-term lease costs	0
Variable lease cost	0
Sublease income	0
Total lease cost	3
Southern Power
Lease cost
Operating lease cost	28
Finance lease cost:
Amortization of ROU assets	0
Interest on lease obligations	0
Total finance lease cost	0
Short-term lease costs	0
Variable lease cost	7
Sublease income	0
Total lease cost	35
Southern Company Gas
Lease cost
Operating lease cost	18
Finance lease cost:
Amortization of ROU assets	0
Interest on lease obligations	0
Total finance lease cost	0
Short-term lease costs	0
Variable lease cost	0
Sublease income	0
Total lease cost	$ 18