Leases - Undiscounted Cash Flows to be Received Under PPAs Accounted for as Operating Leases (Details) $ in Millions	Jun. 30, 2019 USD ($)
Lessor, Lease, Description [Line Items]
2019 (remaining)	$ 75
2020	125
2021	118
2022	109
2023	103
Thereafter	1,142
Total	1,672
GEORGIA POWER CO
Lessor, Lease, Description [Line Items]
2019 (remaining)	13
2020	26
2021	18
2022	8
2023	2
Thereafter	0
Total	67
SOUTHERN POWER CO
Lessor, Lease, Description [Line Items]
2019 (remaining)	52
2020	65
2021	66
2022	68
2023	69
Thereafter	350
Total	670
SOUTHERN Co GAS
Lessor, Lease, Description [Line Items]
2019 (remaining)	17
2020	35
2021	35
2022	34
2023	34
Thereafter	497
Total	$ 652