Leases - Major Categories of Lease Obligations (Details) $ in Millions	Jun. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Lease obligations	$ 2,218
Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	1,072
Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	800
Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	147
Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	54
Other
Lessee, Lease, Description [Line Items]
Lease obligations	145
ALABAMA POWER CO
Lessee, Lease, Description [Line Items]
Lease obligations	190
ALABAMA POWER CO | Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	150
ALABAMA POWER CO | Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	4
ALABAMA POWER CO | Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	1
ALABAMA POWER CO | Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	25
ALABAMA POWER CO | Other
Lessee, Lease, Description [Line Items]
Lease obligations	10
GEORGIA POWER CO
Lessee, Lease, Description [Line Items]
Lease obligations	1,686
GEORGIA POWER CO | Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	1,580
GEORGIA POWER CO | Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	62
GEORGIA POWER CO | Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	3
GEORGIA POWER CO | Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	27
GEORGIA POWER CO | Other
Lessee, Lease, Description [Line Items]
Lease obligations	14
MISSISSIPPI POWER CO
Lessee, Lease, Description [Line Items]
Lease obligations	7
MISSISSIPPI POWER CO | Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	0
MISSISSIPPI POWER CO | Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	2
MISSISSIPPI POWER CO | Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	0
MISSISSIPPI POWER CO | Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	3
MISSISSIPPI POWER CO | Other
Lessee, Lease, Description [Line Items]
Lease obligations	2
SOUTHERN POWER CO
Lessee, Lease, Description [Line Items]
Lease obligations	395
SOUTHERN POWER CO | Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	0
SOUTHERN POWER CO | Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	395
SOUTHERN POWER CO | Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	0
SOUTHERN POWER CO | Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	0
SOUTHERN POWER CO | Other
Lessee, Lease, Description [Line Items]
Lease obligations	0
SOUTHERN Co GAS
Lessee, Lease, Description [Line Items]
Lease obligations	94
SOUTHERN Co GAS | Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	0
SOUTHERN Co GAS | Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	81
SOUTHERN Co GAS | Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	13
SOUTHERN Co GAS | Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	0
SOUTHERN Co GAS | Other
Lessee, Lease, Description [Line Items]
Lease obligations	$ 0