Label	Element	Value
Operating Segments [Member] | Southern Company Gas [Member] | Gas Distribution Operations [Member]
Income Tax Expense (Benefit)	us-gaap_IncomeTaxExpenseBenefit	$ 120,000,000
Income Tax Expense (Benefit)	us-gaap_IncomeTaxExpenseBenefit	145,000,000
Income Tax Expense (Benefit)	us-gaap_IncomeTaxExpenseBenefit	114,000,000
Operating Income (Loss)	us-gaap_OperatingIncomeLoss	655,000,000
Operating Income (Loss)	us-gaap_OperatingIncomeLoss	708,000,000
Operating Income (Loss)	us-gaap_OperatingIncomeLoss	803,000,000
Depreciation and Amortization Excluding Nuclear Fuel	so_DepreciationAndAmortizationExcludingNuclearFuel	482,000,000
Depreciation and Amortization Excluding Nuclear Fuel	so_DepreciationAndAmortizationExcludingNuclearFuel	442,000,000
Depreciation and Amortization Excluding Nuclear Fuel	so_DepreciationAndAmortizationExcludingNuclearFuel	516,000,000
Assets	us-gaap_Assets	22,040,000,000
Assets	us-gaap_Assets	20,917,000,000
Assets	us-gaap_Assets	19,090,000,000
Income (Loss) from Equity Method Investments	us-gaap_IncomeLossFromEquityMethodInvestments	0
Income (Loss) from Equity Method Investments	us-gaap_IncomeLossFromEquityMethodInvestments	0
Income (Loss) from Equity Method Investments	us-gaap_IncomeLossFromEquityMethodInvestments	0
Net Income (Loss) Available to Common Stockholders, Basic	us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic	412,000,000
Net Income (Loss) Available to Common Stockholders, Basic	us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic	390,000,000
Net Income (Loss) Available to Common Stockholders, Basic	us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic	470,000,000
Revenues	us-gaap_Revenues	3,679,000,000
Revenues	us-gaap_Revenues	2,952,000,000
Revenues	us-gaap_Revenues	5,267,000,000
Interest and Debt Expense	us-gaap_InterestAndDebtExpense	207,000,000
Interest and Debt Expense	us-gaap_InterestAndDebtExpense	229,000,000
Interest and Debt Expense	us-gaap_InterestAndDebtExpense	192,000,000
Operating Segments [Member] | Southern Company Gas [Member] | Gas Marketing Services [Member]
Income Tax Expense (Benefit)	us-gaap_IncomeTaxExpenseBenefit	34,000,000
Income Tax Expense (Benefit)	us-gaap_IncomeTaxExpenseBenefit	37,000,000
Income Tax Expense (Benefit)	us-gaap_IncomeTaxExpenseBenefit	28,000,000
Operating Income (Loss)	us-gaap_OperatingIncomeLoss	133,000,000
Operating Income (Loss)	us-gaap_OperatingIncomeLoss	119,000,000
Operating Income (Loss)	us-gaap_OperatingIncomeLoss	125,000,000
Depreciation and Amortization Excluding Nuclear Fuel	so_DepreciationAndAmortizationExcludingNuclearFuel	18,000,000
Depreciation and Amortization Excluding Nuclear Fuel	so_DepreciationAndAmortizationExcludingNuclearFuel	22,000,000
Depreciation and Amortization Excluding Nuclear Fuel	so_DepreciationAndAmortizationExcludingNuclearFuel	16,000,000
Assets	us-gaap_Assets	1,556,000,000
Assets	us-gaap_Assets	1,503,000,000
Assets	us-gaap_Assets	1,616,000,000
Income (Loss) from Equity Method Investments	us-gaap_IncomeLossFromEquityMethodInvestments	0
Income (Loss) from Equity Method Investments	us-gaap_IncomeLossFromEquityMethodInvestments	0
Income (Loss) from Equity Method Investments	us-gaap_IncomeLossFromEquityMethodInvestments	0
Net Income (Loss) Available to Common Stockholders, Basic	us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic	88,000,000
Net Income (Loss) Available to Common Stockholders, Basic	us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic	89,000,000
Net Income (Loss) Available to Common Stockholders, Basic	us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic	94,000,000
Revenues	us-gaap_Revenues	638,000,000
Revenues	us-gaap_Revenues	475,000,000
Revenues	us-gaap_Revenues	408,000,000
Interest and Debt Expense	us-gaap_InterestAndDebtExpense	3,000,000
Interest and Debt Expense	us-gaap_InterestAndDebtExpense	3,000,000
Interest and Debt Expense	us-gaap_InterestAndDebtExpense	3,000,000
Operating Segments [Member] | Southern Company Gas [Member] | Wholesale Gas Services [Member]
Income Tax Expense (Benefit)	us-gaap_IncomeTaxExpenseBenefit	32,000,000
Income Tax Expense (Benefit)	us-gaap_IncomeTaxExpenseBenefit	0
Income Tax Expense (Benefit)	us-gaap_IncomeTaxExpenseBenefit	3,000,000
Operating Income (Loss)	us-gaap_OperatingIncomeLoss	20,000,000
Operating Income (Loss)	us-gaap_OperatingIncomeLoss	241,000,000
Operating Income (Loss)	us-gaap_OperatingIncomeLoss	0
Depreciation and Amortization Excluding Nuclear Fuel	so_DepreciationAndAmortizationExcludingNuclearFuel	0
Depreciation and Amortization Excluding Nuclear Fuel	so_DepreciationAndAmortizationExcludingNuclearFuel	1,000,000
Depreciation and Amortization Excluding Nuclear Fuel	so_DepreciationAndAmortizationExcludingNuclearFuel	0
Assets	us-gaap_Assets	850,000,000
Assets	us-gaap_Assets	0
Assets	us-gaap_Assets	31,000,000
Income (Loss) from Equity Method Investments	us-gaap_IncomeLossFromEquityMethodInvestments	0
Income (Loss) from Equity Method Investments	us-gaap_IncomeLossFromEquityMethodInvestments	0
Income (Loss) from Equity Method Investments	us-gaap_IncomeLossFromEquityMethodInvestments	0
Net Income (Loss) Available to Common Stockholders, Basic	us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic	107,000,000
Net Income (Loss) Available to Common Stockholders, Basic	us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic	14,000,000
Net Income (Loss) Available to Common Stockholders, Basic	us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic	0
Interest and Debt Expense	us-gaap_InterestAndDebtExpense	2,000,000
Interest and Debt Expense	us-gaap_InterestAndDebtExpense	0
Interest and Debt Expense	us-gaap_InterestAndDebtExpense	4,000,000
Operating Segments [Member] | Southern Company Gas [Member] | Gas Pipeline Investments [Member]
Income Tax Expense (Benefit)	us-gaap_IncomeTaxExpenseBenefit	27,000,000
Income Tax Expense (Benefit)	us-gaap_IncomeTaxExpenseBenefit	35,000,000
Income Tax Expense (Benefit)	us-gaap_IncomeTaxExpenseBenefit	33,000,000
Operating Income (Loss)	us-gaap_OperatingIncomeLoss	20,000,000
Operating Income (Loss)	us-gaap_OperatingIncomeLoss	21,000,000
Operating Income (Loss)	us-gaap_OperatingIncomeLoss	21,000,000
Depreciation and Amortization Excluding Nuclear Fuel	so_DepreciationAndAmortizationExcludingNuclearFuel	5,000,000
Depreciation and Amortization Excluding Nuclear Fuel	so_DepreciationAndAmortizationExcludingNuclearFuel	5,000,000
Depreciation and Amortization Excluding Nuclear Fuel	so_DepreciationAndAmortizationExcludingNuclearFuel	5,000,000
Assets	us-gaap_Assets	1,577,000,000
Assets	us-gaap_Assets	1,467,000,000
Assets	us-gaap_Assets	1,597,000,000
Income (Loss) from Equity Method Investments	us-gaap_IncomeLossFromEquityMethodInvestments	148,000,000
Income (Loss) from Equity Method Investments	us-gaap_IncomeLossFromEquityMethodInvestments	141,000,000
Income (Loss) from Equity Method Investments	us-gaap_IncomeLossFromEquityMethodInvestments	50,000,000
Net Income (Loss) Available to Common Stockholders, Basic	us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic	19,000,000
Net Income (Loss) Available to Common Stockholders, Basic	us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic	99,000,000
Net Income (Loss) Available to Common Stockholders, Basic	us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic	107,000,000
Revenues	us-gaap_Revenues	32,000,000
Revenues	us-gaap_Revenues	32,000,000
Revenues	us-gaap_Revenues	32,000,000
Interest and Debt Expense	us-gaap_InterestAndDebtExpense	25,000,000
Interest and Debt Expense	us-gaap_InterestAndDebtExpense	27,000,000
Interest and Debt Expense	us-gaap_InterestAndDebtExpense	$ 29,000,000