Leases - Lease Costs (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Lease cost
Operating lease cost	$ 69
Finance lease cost:
Amortization of ROU assets	7
Interest on lease obligations	3
Total finance lease cost	10
Short-term lease costs	14
Variable lease cost	19
Sublease income	0
Total lease cost	112
ALABAMA POWER CO
Lease cost
Operating lease cost	7
Finance lease cost:
Amortization of ROU assets	0
Interest on lease obligations	0
Total finance lease cost	0
Short-term lease costs	5
Variable lease cost	0
Sublease income	0
Total lease cost	12
GEORGIA POWER CO
Lease cost
Operating lease cost	49
Finance lease cost:
Amortization of ROU assets	4
Interest on lease obligations	4
Total finance lease cost	8
Short-term lease costs	3
Variable lease cost	16
Sublease income	0
Total lease cost	76
MISSISSIPPI POWER CO
Lease cost
Operating lease cost	1
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	1
SOUTHERN POWER CO
Lease cost
Operating lease cost	7
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	1
Sublease income	0
Total lease cost	8
SOUTHERN Co GAS
Lease cost
Operating lease cost	4
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	$ 4