Leases - Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Lease cost
Operating lease cost	$ 94	$ 243
Finance lease cost:
Amortization of ROU assets	7	21
Interest on lease obligations	3	9
Total finance lease cost	10	30
Short-term lease costs	9	39
Variable lease cost	33	81
Sublease income		(1)
Total lease cost	146	392
ALABAMA POWER CO
Lease cost
Operating lease cost	29	49
Finance lease cost:
Amortization of ROU assets	0	1
Interest on lease obligations	0	0
Total finance lease cost	0	1
Short-term lease costs	4	15
Variable lease cost	4	6
Sublease income		(1)
Total lease cost	37	70
GEORGIA POWER CO
Lease cost
Operating lease cost	53	154
Finance lease cost:
Amortization of ROU assets	4	11
Interest on lease obligations	4	14
Total finance lease cost	8	25
Short-term lease costs	5	17
Variable lease cost	26	67
Sublease income		0
Total lease cost	92	263
MISSISSIPPI POWER CO
Lease cost
Operating lease cost	1	2
Finance lease cost:
Amortization of ROU assets	0	0
Interest on lease obligations	0	0
Total finance lease cost	0	0
Short-term lease costs	0	0
Variable lease cost	0	0
Sublease income		0
Total lease cost	1	2
SOUTHERN POWER CO
Lease cost
Operating lease cost	7	21
Finance lease cost:
Amortization of ROU assets	0	0
Interest on lease obligations	0	0
Total finance lease cost	0	0
Short-term lease costs	0	0
Variable lease cost	1	3
Sublease income		0
Total lease cost	8	24
SOUTHERN Co GAS
Lease cost
Operating lease cost	5	14
Finance lease cost:
Amortization of ROU assets	0	0
Interest on lease obligations	0	0
Total finance lease cost	0	0
Short-term lease costs	0	0
Variable lease cost	0	0
Sublease income		0
Total lease cost	$ 5	$ 14