Commitments - Estimated Long-term Obligations (Details) $ in Millions	Dec. 31, 2018 USD ($)
Minimum Lease Payments, Operating Leases [Abstract]
2019	$ 156
2020	134
2021	110
2022	98
2023	79
2024 and thereafter	1,040
Total	1,617
Alabama Power
Minimum Lease Payments, Operating Leases [Abstract]
2019	12
2020	10
2021	7
2022	6
2023	3
2024 and thereafter	1
Total	39
Georgia Power
Minimum Lease Payments, Operating Leases [Abstract]
2019	23
2020	18
2021	9
2022	6
2023	5
2024 and thereafter	13
Total	74
Mississippi Power
Minimum Lease Payments, Operating Leases [Abstract]
2019	3
2020	2
2021	1
2022	1
2023	1
2024 and thereafter	2
Total	10
Southern Power
Minimum Lease Payments, Operating Leases [Abstract]
2019	23
2020	24
2021	24
2022	24
2023	26
2024 and thereafter	874
Total	995
Southern Company Gas
Minimum Lease Payments, Operating Leases [Abstract]
2019	18
2020	16
2021	15
2022	13
2023	10
2024 and thereafter	34
Total	106
Non-Affiliate Operating Lease PPA
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2019	161
2020	164
2021	168
2022	171
2023	127
2024 and thereafter	642
Total	1,433
Non-Affiliate Operating Lease PPA \| Alabama Power
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2019	41
2020	42
2021	44
2022	46
2023	0
2024 and thereafter	0
Total	173
Non-Affiliate Operating Lease PPA \| Georgia Power
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2019	120
2020	122
2021	124
2022	125
2023	127
2024 and thereafter	642
Total	1,260
Affiliate Capital Lease PPA \| Georgia Power
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2019	23
2020	23
2021	24
2022	24
2023	25
2024 and thereafter	158
Total	277
Minimum Lease Payments, Capital Leases [Abstract]
Less: amounts representing executory costs	42
Net minimum lease payments	235
Less: amounts representing interest	105
Present value of net minimum lease payments	130
Affiliate Operating Lease PPA \| Georgia Power
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2019	64
2020	65
2021	66
2022	68
2023	69
2024 and thereafter	349
Total	$ 681

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Amounts to be paid by lessee to lessor for maintenance, insurance, and tax expenses related to the leased asset.

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Amount of minimum lease payments for capital leases net of executory costs, which include amounts paid by the lessee to the lessor for insurance, maintenance and taxes.

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Present value of minimum lease payments for capital leases net of executory costs, including amounts paid by the lessee to the lessor for insurance, maintenance and taxes.

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Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of the recorded obligation to transfer funds in the future for fixed or minimum amounts or quantities of goods or services at fixed or minimum prices (for example, as in take-or-pay contracts or throughput contracts).

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