Leases - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($) MW
Lessee, Lease, Description [Line Items]
Remaining terms	14 years 4 months 24 days
Minimum lease payments	$ 2,721
Real estate | Maximum
Lessee, Lease, Description [Line Items]
Remaining terms	25 years
Communication towers | Maximum
Lessee, Lease, Description [Line Items]
Lessee, lease term	10 years
Lessee, renewal period	20 years
Fuel cells | Maximum
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	15 years
GEORGIA POWER CO
Lessee, Lease, Description [Line Items]
Remaining terms	10 years 4 months 24 days
Lease obligations	$ 1,430
Minimum lease payments	$ 1,810
GEORGIA POWER CO | Real estate | Maximum
Lessee, Lease, Description [Line Items]
Remaining terms	25 years
GEORGIA POWER CO | Electric generating units | Affiliate
Lessee, Lease, Description [Line Items]
Lease obligations	$ 625
GEORGIA POWER CO | Electric generating units | Minimum
Lessee, Lease, Description [Line Items]
Remaining terms	3 years
GEORGIA POWER CO | Electric generating units | Maximum
Lessee, Lease, Description [Line Items]
Remaining terms	18 years
GEORGIA POWER CO | Outdoor lighting | Maximum
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	5 years
SOUTHERN Co GAS
Lessee, Lease, Description [Line Items]
Remaining terms	9 years 7 months 6 days
Lease obligations	$ 91
Minimum lease payments	$ 111
SOUTHERN Co GAS | Maximum
Lessee, Lease, Description [Line Items]
Lessor, remaining term	24 years
SOUTHERN Co GAS | Real estate | Maximum
Lessee, Lease, Description [Line Items]
Remaining terms	25 years
SOUTHERN POWER CO
Lessee, Lease, Description [Line Items]
Remaining terms	33 years 2 months 12 days
Lease obligations	$ 395
Minimum lease payments	$ 947
SOUTHERN POWER CO | Land | Maximum
Lessee, Lease, Description [Line Items]
Lessee, lease term	47 years
SOUTHERN POWER CO | Electric generating units | Maximum
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	28 years
ALABAMA POWER CO
Lessee, Lease, Description [Line Items]
Remaining terms	3 years 4 months 24 days
Lease obligations	$ 158
PPA, additional generating capacity (in MWs) | MW	640
Minimum lease payments	$ 169
ALABAMA POWER CO | Electric generating units
Lessee, Lease, Description [Line Items]
Minimum lease payments	$ 95
ALABAMA POWER CO | Electric generating units | Minimum
Lessee, Lease, Description [Line Items]
Remaining terms	3 years
ALABAMA POWER CO | Electric generating units | Maximum
Lessee, Lease, Description [Line Items]
Remaining terms	18 years
ALABAMA POWER CO | Outdoor lighting | Maximum
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	5 years
MISSISSIPPI POWER CO
Lessee, Lease, Description [Line Items]
Remaining terms	6 years 9 months 18 days
Lease obligations	$ 7
Minimum lease payments	$ 8
MISSISSIPPI POWER CO | Electric generating units | Maximum
Lessee, Lease, Description [Line Items]
Lessor, lease term, sales-type lease	20 years
MISSISSIPPI POWER CO | Outdoor lighting | Maximum
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	5 years
Traditional Electric Operating Companies | Outdoor lighting | Maximum
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	7 years