Leases - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Remaining terms	13 years 6 months
Total estimate obligations of leases that have not yet commenced	$ 77
Maximum
Lessee, Lease, Description [Line Items]
Lease term, lease not yet commenced	30 years
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 1 month
Lease obligations	$ 1,543
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	$ 670
GEORGIA POWER CO | Electric generating units | Minimum
Lessee, Lease, Description [Line Items]
Remaining terms	4 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
Lease obligations	$ 84
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 8 months
Lease obligations	$ 393
Total estimate obligations of leases that have not yet commenced	$ 77
SOUTHERN POWER CO | Maximum
Lessee, Lease, Description [Line Items]
Lease term, lease not yet commenced	30 years
SOUTHERN POWER CO | Land | Maximum
Lessee, Lease, Description [Line Items]
Lessee, lease term	48 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 9 months
Lease obligations	$ 194
ALABAMA POWER CO | Electric generating units | Minimum
Lessee, Lease, Description [Line Items]
Remaining terms	4 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
Lease obligations	$ 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