Commitments - Estimated Long-term obligations (Details) $ in Millions	Dec. 31, 2017 USD ($)
Minimum Lease Payments, Operating Leases [Abstract]
2018	$ 149
2019	124
2020	108
2021	95
2022	83
2023 and thereafter	968
Total	1,527
ALABAMA POWER CO
Minimum Lease Payments, Operating Leases [Abstract]
2018	21
2019	22
2020	18
2021	14
2022	10
2023 and thereafter	20
Total	105
Future minimum sublease rentals	3
SOUTHERN POWER CO
Minimum Lease Payments, Operating Leases [Abstract]
2019	22
2020	22
2021	23
2022	23
2023 and thereafter	815
GEORGIA POWER CO
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2018	219
2019	220
2020	216
2021	220
2022	221
2023 and thereafter	1,405
Total	2,501
Minimum Lease Payments, Operating Leases [Abstract]
2018	24
2019	22
2020	20
2021	17
2022	14
2023 and thereafter	44
Total	141
GULF POWER CO
Minimum Lease Payments, Operating Leases [Abstract]
2018	9
2019	2
2020	2
2021	1
2022	1
2023 and thereafter	5
Total	20
MISSISSIPPI POWER CO
Minimum Lease Payments, Operating Leases [Abstract]
2018	3
2019	3
2020	3
2021	2
2022	2
2023 and thereafter	7
Total	20
SOUTHERN Co GAS
Minimum Lease Payments, Operating Leases [Abstract]
2018	17
2019	16
2020	16
2021	15
2022	13
2023 and thereafter	26
Total	103
Affiliate Operating Lease PPA \| MISSISSIPPI POWER CO
Minimum Lease Payments, Operating Leases [Abstract]
2018	2
2019	2
2020	2
2021	2
2022	2
2023 and thereafter	7
Total	17
Affiliate Operating Lease \| ALABAMA POWER CO
Minimum Lease Payments, Operating Leases [Abstract]
2018	8
2019	10
2020	8
2021	7
2022	5
2023 and thereafter	16
Total	54
Barges & Railcars
Minimum Lease Payments, Operating Leases [Abstract]
2018	21
2019	11
2020	9
2021	8
2022	6
2023 and thereafter	5
Total	60
Barges & Railcars \| GEORGIA POWER CO
Minimum Lease Payments, Operating Leases [Abstract]
2018	14
2019	11
2020	9
2021	8
2022	6
2023 and thereafter	11
Total	59
Barges & Railcars \| GULF POWER CO
Minimum Lease Payments, Operating Leases [Abstract]
2018	2
2019	1
2020	1
2021	1
2022	1
2023 and thereafter	4
Total	10
Other
Minimum Lease Payments, Operating Leases [Abstract]
2018	128
2019	113
2020	99
2021	87
2022	77
2023 and thereafter	963
Total	1,467
Other \| GULF POWER CO
Minimum Lease Payments, Operating Leases [Abstract]
2018	7
2019	1
2020	1
2021	0
2022	0
2023 and thereafter	1
Total	10
Railcars \| ALABAMA POWER CO
Minimum Lease Payments, Operating Leases [Abstract]
2018	7
2019	7
2020	7
2021	6
2022	5
2023 and thereafter	4
Total	36
Vehicles & Other \| ALABAMA POWER CO
Minimum Lease Payments, Operating Leases [Abstract]
2018	6
2019	5
2020	3
2021	1
2022	0
2023 and thereafter	0
Total	15
Non-Affiliate Operating Lease \| MISSISSIPPI POWER CO
Minimum Lease Payments, Operating Leases [Abstract]
2018	1
2019	1
2020	1
2021	0
2022	0
2023 and thereafter	0
Total	3
Operating Lease PPA
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2018	247
2019	250
2020	247
2021	249
2022	252
2023 and thereafter	806
Total	2,051
Non-Affiliate Operating Lease PPA \| GEORGIA POWER CO
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2018	127
2019	128
2020	124
2021	125
2022	126
2023 and thereafter	773
Total	1,403
Plant Vogtle (nuclear) Units 1 and 2 \| GEORGIA POWER CO
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2018	7
2019	6
2020	4
2021	5
2022	4
2023 and thereafter	38
Total	64
Affiliate Capital Lease PPA \| GEORGIA POWER CO
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2018	23
2019	23
2020	23
2021	24
2022	24
2023 and thereafter	182
Total	299
Minimum Lease Payments, Capital Leases [Abstract]
Less: amounts representing executory costs	45
Net minimum lease payments	254
Less: amounts representing interest	120
Present value of net minimum lease payments	134
Affiliate Operating Lease PPA \| GEORGIA POWER CO
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2018	62
2019	63
2020	65
2021	66
2022	67
2023 and thereafter	412
Total	735
Minimum Lease Payments, Operating Leases [Abstract]
2018	10
2019	11
2020	11
2021	9
2022	8
2023 and thereafter	33
Total	82
Purchased Power \| ALABAMA POWER CO
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2018	41
2019	43
2020	44
2021	46
2022	47
2023 and thereafter	0
Total	221
Purchased Power \| GULF POWER CO
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2018	79
2019	79
2020	79
2021	79
2022	79
2023 and thereafter	33
Total	428
Other
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2018	7
2019	6
2020	4
2021	5
2022	4
2023 and thereafter	38
Total	$ 64

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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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Minimum payments receivable in the future under noncancelable subleases.

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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 required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fourth 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 third 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 second 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 after 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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Amount of the recorded unconditional purchase obligation maturing after 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 unconditional purchase obligation maturing in the fourth 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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