Income Taxes	3 Months Ended
Mar. 31, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES See Note 5 to the financial statements of each registrant in Item 8 of the Form 10-K for additional tax information. Federal Tax Reform Legislation Following the enactment of the Tax Reform Legislation, the SEC staff issued Staff Accounting Bulletin 118 – "Income Tax Accounting Implications of the Tax Cuts and Jobs Act" (SAB 118), which provides for a measurement period of up to one year from the enactment date to complete accounting under GAAP for the tax effects of the legislation. Due to the complex and comprehensive nature of the enacted tax law changes, and their application under GAAP, the registrants consider all amounts recorded in the financial statements as a result of the Tax Reform Legislation to be "provisional" as discussed in SAB 118 and subject to revision. Each of the registrants are awaiting additional guidance from industry and income tax authorities in order to finalize its accounting. The ultimate impact of the Tax Reform Legislation on deferred income tax assets and liabilities and the related regulatory assets and liabilities cannot be determined at this time. See Note (B) under "Regulatory Matters" for additional information. Current and Deferred Income Taxes Tax Credit Carryforwards Southern Company had federal ITC and PTC carryforwards (primarily related to Southern Power) totaling $2.3 billion as of March 31, 2018 compared to $2.1 billion as of December 31, 2017. The federal ITC carryforwards begin expiring in 2034 but are expected to be fully utilized by 2027. The PTC carryforwards begin expiring in 2032 but are expected to be utilized by 2027. The estimated tax credit utilization reflects a 2018 abandonment loss related to certain Kemper County energy facility expenditures. The expected utilization of tax credit carryforwards could be further delayed by numerous factors, including the acquisition of additional renewable projects and increased generation at existing wind facilities. The ultimate outcome of these matters cannot be determined at this time. Effective Tax Rate Each registrant's effective tax rate for the three months ended March 31, 2018 varied significantly as compared to the corresponding period in 2017 due to the 14% lower 2018 federal tax rate resulting from the Tax Reform Legislation. Southern Company Southern Company's effective tax rate is typically lower than the statutory rate due to employee stock plans' dividend deduction, non-taxable AFUDC equity, and federal income tax benefits from ITCs and PTCs. Southern Company's effective tax rate was 10.8% for the three months ended March 31, 2018 compared to 32.1% for the corresponding period in 2017. The effective tax rate decrease was primarily due to the lower federal tax rate in 2018 as a result of the Tax Reform Legislation, as well as net state income tax benefits related to changes in state apportionment rates arising from the reorganization of Southern Power's legal entities as discussed further herein. Southern Company recognizes PTCs when wind energy is generated and sold (using the prescribed KWH rate in applicable federal and state statutes), which may differ significantly from amounts computed on a quarterly basis using an overall estimated annual effective income tax rate. Southern Company uses this method of recognition since the amount of PTCs can be significantly impacted by wind generation. This method can significantly affect the effective income tax rate for the period depending on the amount of pretax income. Mississippi Power Mississippi Power's effective tax (benefit) rate was (34.7)% for the three months ended March 31, 2018 compared to (58.7)% for the corresponding period in 2017. In addition to the reduction in the federal corporate income tax rate as a result of the Tax Reform Legislation, the effective tax rate increase was primarily due to lower estimated losses on the Kemper IGCC for the three months ended March 31, 2018 compared to the corresponding period in 2017, partially offset by non-deductible AFUDC equity in 2017. Southern Power Southern Power's effective tax (benefit) rate was (647.0)% for the three months ended March 31, 2018 compared to (385.9)% for the corresponding period in 2017. In addition to the reduction in the federal corporate income tax rate as a result of the Tax Reform Legislation, the effective tax rate decrease was primarily due to net state income tax benefits related to certain changes in apportionment rates arising from the reorganization of Southern Power's legal entities as described below. Southern Power recognizes PTCs when wind energy is generated and sold (using the prescribed KWH rate in applicable federal and state statutes), which may differ significantly from amounts computed on a quarterly basis using an overall estimated annual effective income tax rate. Southern Power uses this method of recognition since the amount of PTCs can be significantly impacted by wind generation. This method can significantly affect the effective income tax rate for the period depending on the amount of pretax income. Legal Entity Reorganization In March 2018, Southern Power substantially completed a legal entity reorganization of various direct and indirect subsidiaries that own and operate substantially all of its solar facilities, including certain subsidiaries owned in partnership with various third parties. The reorganization resulted in net state tax benefits related to certain changes in apportionment rates totaling approximately $50 million, which were recorded in the first quarter 2018. In April 2018, Southern Power completed the final stage of the reorganization resulting in additional net state tax benefits of approximately $4 million. Unrecognized Tax Benefits See Note 5 to the financial statements of each registrant under "Unrecognized Tax Benefits" in Item 8 of the Form 10-K for additional information. The registrants had no unrecognized tax benefits as of March 31, 2018. It is reasonably possible that the amount of the unrecognized tax benefits could change within 12 months. The settlement of federal and state audits could impact the balances significantly. At this time, an estimate of the range of reasonably possible outcomes cannot be determined.

INCOME TAXES

See Note 5 to the financial statements of each registrant in Item 8 of the Form 10-K for additional tax information.

Federal Tax Reform Legislation

Following the enactment of the Tax Reform Legislation, the SEC staff issued Staff Accounting Bulletin 118 – "Income Tax Accounting Implications of the Tax Cuts and Jobs Act" (SAB 118), which provides for a measurement period of up to one year from the enactment date to complete accounting under GAAP for the tax effects of the legislation. Due to the complex and comprehensive nature of the enacted tax law changes, and their application under GAAP, the registrants consider all amounts recorded in the financial statements as a result of the Tax Reform Legislation to be "provisional" as discussed in SAB 118 and subject to revision. Each of the registrants are awaiting additional guidance from industry and income tax authorities in order to finalize its accounting. The ultimate impact of the Tax Reform Legislation on deferred income tax assets and liabilities and the related regulatory assets and liabilities cannot be determined at this time. See Note (B) under "Regulatory Matters" for additional information.

Current and Deferred Income Taxes

Tax Credit Carryforwards

Southern Company had federal ITC and PTC carryforwards (primarily related to Southern Power) totaling $2.3 billion as of March 31, 2018 compared to $2.1 billion as of December 31, 2017.

The federal ITC carryforwards begin expiring in 2034 but are expected to be fully utilized by 2027. The PTC carryforwards begin expiring in 2032 but are expected to be utilized by 2027. The estimated tax credit utilization reflects a 2018 abandonment loss related to certain Kemper County energy facility expenditures. The expected utilization of tax credit carryforwards could be further delayed by numerous factors, including the acquisition of additional renewable projects and increased generation at existing wind facilities. The ultimate outcome of these matters cannot be determined at this time.

Effective Tax Rate

Each registrant's effective tax rate for the three months ended March 31, 2018 varied significantly as compared to the corresponding period in 2017 due to the 14% lower 2018 federal tax rate resulting from the Tax Reform Legislation.

Southern Company

Southern Company's effective tax rate is typically lower than the statutory rate due to employee stock plans' dividend deduction, non-taxable AFUDC equity, and federal income tax benefits from ITCs and PTCs.

Southern Company's effective tax rate was 10.8% for the three months ended March 31, 2018 compared to 32.1% for the corresponding period in 2017. The effective tax rate decrease was primarily due to the lower federal tax rate in 2018 as a result of the Tax Reform Legislation, as well as net state income tax benefits related to changes in state apportionment rates arising from the reorganization of Southern Power's legal entities as discussed further herein.

Southern Company recognizes PTCs when wind energy is generated and sold (using the prescribed KWH rate in applicable federal and state statutes), which may differ significantly from amounts computed on a quarterly basis using an overall estimated annual effective income tax rate. Southern Company uses this method of recognition since the amount of PTCs can be significantly impacted by wind generation. This method can significantly affect the effective income tax rate for the period depending on the amount of pretax income.

Mississippi Power

Mississippi Power's effective tax (benefit) rate was (34.7)% for the three months ended March 31, 2018 compared to (58.7)% for the corresponding period in 2017. In addition to the reduction in the federal corporate income tax rate as a result of the Tax Reform Legislation, the effective tax rate increase was primarily due to lower estimated losses on the Kemper IGCC for the three months ended March 31, 2018 compared to the corresponding period in 2017, partially offset by non-deductible AFUDC equity in 2017.

Southern Power

Southern Power's effective tax (benefit) rate was (647.0)% for the three months ended March 31, 2018 compared to (385.9)% for the corresponding period in 2017. In addition to the reduction in the federal corporate income tax rate as a result of the Tax Reform Legislation, the effective tax rate decrease was primarily due to net state income tax benefits related to certain changes in apportionment rates arising from the reorganization of Southern Power's legal entities as described below.

Southern Power recognizes PTCs when wind energy is generated and sold (using the prescribed KWH rate in applicable federal and state statutes), which may differ significantly from amounts computed on a quarterly basis using an overall estimated annual effective income tax rate. Southern Power uses this method of recognition since the amount of PTCs can be significantly impacted by wind generation. This method can significantly affect the effective income tax rate for the period depending on the amount of pretax income.

Legal Entity Reorganization

In March 2018, Southern Power substantially completed a legal entity reorganization of various direct and indirect subsidiaries that own and operate substantially all of its solar facilities, including certain subsidiaries owned in partnership with various third parties. The reorganization resulted in net state tax benefits related to certain changes in apportionment rates totaling approximately $50 million, which were recorded in the first quarter 2018. In April 2018, Southern Power completed the final stage of the reorganization resulting in additional net state tax benefits of approximately $4 million.

Unrecognized Tax Benefits

See Note 5 to the financial statements of each registrant under "Unrecognized Tax Benefits" in Item 8 of the Form 10-K for additional information.

The registrants had no unrecognized tax benefits as of March 31, 2018. It is reasonably possible that the amount of the unrecognized tax benefits could change within 12 months. The settlement of federal and state audits could impact the balances significantly. At this time, an estimate of the range of reasonably possible outcomes cannot be determined.