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Fair Value Measurements - Textual (Details) (Georgia Power [Member], USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Fair Value, Option, Quantitative Disclosures [Line Items]  
Notices Of Withdrawal Foreign Equity Funds 20.00%so_NoticesOfWithdrawalForeignEquityFunds
Minimum [Member]  
Fair Value, Option, Quantitative Disclosures [Line Items]  
Withdrawal Of Foreign Equity Fund Investment 1so_WithdrawalOfForeignEquityFundInvestment
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Foreign Equity Fund Investment 10so_ForeignEquityFundInvestment
/ dei_LegalEntityAxis
= so_GeorgiaPowerMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Maximum [Member]  
Fair Value, Option, Quantitative Disclosures [Line Items]  
Period Of Funds Maturity 90 days