Commitments - Textuals (Details) MMBTU in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2017 USD ($) MMBTU	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2013
Recorded Unconditional Purchase Obligation [Line Items]
Fuel expense			$ 4,400,000,000	$ 4,361,000,000	$ 4,750,000,000
Expense under purchase power agreements accounted for as operating leases			235,000,000	232,000,000	227,000,000
Operating leases rent expense			176,000,000	169,000,000	130,000,000
Operating leases, future minimum lease payments due			1,527,000,000
Leasing commitment, 2018			149,000,000
Leasing commitment, 2019			124,000,000
Leasing commitment, 2020			108,000,000
Leasing commitment, 2021			95,000,000
Leasing commitment, 2023 and thereafter			968,000,000
Senior notes	$ 33,000,000,000		35,100,000,000	33,000,000,000
2022			83,000,000
Barges & Railcars
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases, future minimum lease payments due			60,000,000
Leasing commitment, 2018			21,000,000
Leasing commitment, 2019			11,000,000
Leasing commitment, 2020			9,000,000
Leasing commitment, 2021			8,000,000
Leasing commitment, 2023 and thereafter			5,000,000
2022			6,000,000
ALABAMA POWER CO
Recorded Unconditional Purchase Obligation [Line Items]
Fuel expense			1,225,000,000	1,297,000,000	1,342,000,000
Expense under purchase power agreements accounted for as operating leases			41,000,000	42,000,000	38,000,000
Operating leases rent expense			25,000,000	18,000,000	19,000,000
Operating leases, future minimum lease payments due			105,000,000
Leasing commitment, 2018			21,000,000
Leasing commitment, 2019			22,000,000
Leasing commitment, 2020			18,000,000
Leasing commitment, 2021			14,000,000
Leasing commitment, 2023 and thereafter			20,000,000
Long-term pollution control bonds	1,100,000,000		$ 1,060,000,000	1,100,000,000
Percent ownership			14.00%
2022			$ 10,000,000
ALABAMA POWER CO | Barges & Railcars
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases rent expense			11,000,000	14,000,000	13,000,000
ALABAMA POWER CO | Residual Value, Leased Property
Recorded Unconditional Purchase Obligation [Line Items]
Leasing commitment, 2018			0
Leasing commitment, 2019			0
Leasing commitment, 2020			0
Leasing commitment, 2021			0
Leasing commitment, 2023 and thereafter			12,000,000
2022			0
GEORGIA POWER CO
Recorded Unconditional Purchase Obligation [Line Items]
Fuel expense			1,671,000,000	1,807,000,000	2,033,000,000
Operating leases rent expense			31,000,000	28,000,000	29,000,000
Operating leases, future minimum lease payments due			$ 141,000,000
Period of service for gas transportation supplier			1 year
Maximum guarantee			$ 43,000,000
Leasing commitment, 2018			24,000,000
Leasing commitment, 2019			22,000,000
Leasing commitment, 2020			20,000,000
Leasing commitment, 2021			17,000,000
Leasing commitment, 2023 and thereafter			44,000,000
Long-term pollution control bonds	1,800,000,000		1,800,000,000	1,800,000,000
Senior notes	6,200,000,000		7,100,000,000	6,200,000,000
Capacity payments			9,000,000	11,000,000	10,000,000
Deferred capacity expense	217,000,000		$ 199,000,000	217,000,000	203,000,000
Percentage of minimum lease payments			100.00%
Operating leases, contingent rent expense			$ 73,000,000	39,000,000	8,000,000
2022			$ 14,000,000
GEORGIA POWER CO | Plant McIntosh
Recorded Unconditional Purchase Obligation [Line Items]
Period of service for gas transportation supplier						15 years
GEORGIA POWER CO | MEAG Power
Recorded Unconditional Purchase Obligation [Line Items]
Percent ownership			5.00%
GEORGIA POWER CO | ALABAMA POWER CO | Payment Guarantee
Recorded Unconditional Purchase Obligation [Line Items]
Long-term pollution control bonds			$ 25,000,000
GEORGIA POWER CO | ALABAMA POWER CO | Financial Guarantee
Recorded Unconditional Purchase Obligation [Line Items]
Senior notes			100,000,000
GEORGIA POWER CO | Barges & Railcars
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases, future minimum lease payments due			59,000,000
Leasing commitment, 2018			14,000,000
Leasing commitment, 2019			11,000,000
Leasing commitment, 2020			9,000,000
Leasing commitment, 2021			8,000,000
Leasing commitment, 2023 and thereafter			11,000,000
2022			6,000,000
GEORGIA POWER CO | Residual Value, Leased Property | 2018
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases, future minimum lease payments due			32,000,000
GULF POWER CO
Recorded Unconditional Purchase Obligation [Line Items]
Fuel expense			427,000,000	432,000,000	445,000,000
Expense under purchase power agreements accounted for as operating leases			75,000,000	75,000,000
Operating leases rent expense			10,000,000	9,000,000	14,000,000
Operating leases, future minimum lease payments due			20,000,000
Leasing commitment, 2018			9,000,000
Leasing commitment, 2019			2,000,000
Leasing commitment, 2020			2,000,000
Leasing commitment, 2021			1,000,000
Leasing commitment, 2023 and thereafter			5,000,000
Long-term pollution control bonds	309,000,000		309,000,000	309,000,000
Senior notes	777,000,000		990,000,000	777,000,000
Deferred capacity expense	119,000,000		97,000,000	119,000,000
2022			1,000,000
GULF POWER CO | Barges & Railcars
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases, future minimum lease payments due			10,000,000
Leasing commitment, 2018			2,000,000
Leasing commitment, 2019			1,000,000
Leasing commitment, 2020			1,000,000
Leasing commitment, 2021			1,000,000
Leasing commitment, 2023 and thereafter			4,000,000
2022			1,000,000
GULF POWER CO | Barges & Railcars | Plant Daniel
Recorded Unconditional Purchase Obligation [Line Items]
Fuel cost recovery clause				2,000,000
GULF POWER CO | Barge Transportation | Plant Crist and Plant Smith
Recorded Unconditional Purchase Obligation [Line Items]
Leasing commitment, 2018			6,000,000
Leasing commitment, 2019			5,000,000
Fuel cost recovery clause			7,000,000	5,000,000	10,000,000
MISSISSIPPI POWER CO
Recorded Unconditional Purchase Obligation [Line Items]
Fuel expense			395,000,000	343,000,000	443,000,000
Operating leases rent expense			3,000,000	3,000,000	5,000,000
Operating leases, future minimum lease payments due			20,000,000
Leasing commitment, 2018			3,000,000
Leasing commitment, 2019			3,000,000
Leasing commitment, 2020			3,000,000
Leasing commitment, 2021			2,000,000
Leasing commitment, 2023 and thereafter			7,000,000
Long-term pollution control bonds	83,000,000		83,000,000	83,000,000
Senior notes	790,000,000		$ 755,000,000	790,000,000
Company's share of the leases			50.00%
Fuel cost recovery clause			$ 1,000,000	2,000,000	2,000,000
2022			$ 2,000,000
MISSISSIPPI POWER CO | Plant Daniel
Recorded Unconditional Purchase Obligation [Line Items]
Company's share of the leases			50.00%
SOUTHERN POWER CO
Recorded Unconditional Purchase Obligation [Line Items]
Fuel expense			$ 621,000,000	456,000,000	441,000,000
Operating leases rent expense			29,000,000	22,000,000	$ 7,000,000
Leasing commitment, 2019			22,000,000
Leasing commitment, 2020			22,000,000
Leasing commitment, 2021			23,000,000
Leasing commitment, 2023 and thereafter			815,000,000
Senior notes	5,300,000,000		5,500,000,000	5,300,000,000
2022			23,000,000
SOUTHERN Co GAS
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases rent expense			15,000,000
Operating leases, future minimum lease payments due			103,000,000
Leasing commitment, 2018			17,000,000
Leasing commitment, 2019			16,000,000
Leasing commitment, 2020			16,000,000
Leasing commitment, 2021			15,000,000
Leasing commitment, 2023 and thereafter			26,000,000
Senior notes	3,700,000,000		4,200,000,000	$ 3,700,000,000
2022			13,000,000
Alabama Power and Georgia Power
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases, future minimum lease payments due			44,000,000
Tropic Equipment Leasing Inc | Financial Guarantee
Recorded Unconditional Purchase Obligation [Line Items]
Maximum guarantee			$ 1,000,000
Nicor Gas and Southstar
Recorded Unconditional Purchase Obligation [Line Items]
Natural gas pipeline capacity | MMBTU			35
Long-term purchase commitment amount			$ 101,000,000
Predecessor | SOUTHERN Co GAS
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases rent expense	$ 6,000,000	$ 12,000,000	$ 8,000,000
Minimum | ALABAMA POWER CO
Recorded Unconditional Purchase Obligation [Line Items]
Lessee, Operating Lease, Term of Contract			5 years
Minimum | GEORGIA POWER CO
Recorded Unconditional Purchase Obligation [Line Items]
Lessee, Operating Lease, Term of Contract			5 years
Minimum | GULF POWER CO
Recorded Unconditional Purchase Obligation [Line Items]
Lessee, Operating Lease, Term of Contract			5 years
Maximum | ALABAMA POWER CO
Recorded Unconditional Purchase Obligation [Line Items]
Lessee, Operating Lease, Term of Contract			10 years
Lessee, Operating Lease, Renewal Term			20 years
Maximum | GEORGIA POWER CO
Recorded Unconditional Purchase Obligation [Line Items]
Lessee, Operating Lease, Term of Contract			10 years
Lessee, Operating Lease, Renewal Term			20 years
Maximum | GULF POWER CO
Recorded Unconditional Purchase Obligation [Line Items]
Lessee, Operating Lease, Term of Contract			10 years
Lessee, Operating Lease, Renewal Term			5 years
Maximum | MISSISSIPPI POWER CO
Recorded Unconditional Purchase Obligation [Line Items]
Lessee, Operating Lease, Term of Contract			10 years
Lessee, Operating Lease, Renewal Term			20 years