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Retirement Benefits - Schedule of Health Care Cost Trend Rates (Details)
12 Months Ended
Dec. 31, 2016
USD ($)
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]  
Benefit obligation, 1 percent increase $ 128,000,000
Benefit obligation, 1 percent decrease 110,000,000
Service and interest costs, 1 percent increase 4,000,000
Service and interest costs, 1 percent decrease $ 3,000,000
Other postretirement benefit plans | Pre-65  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 6.50%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Other postretirement benefit plans | Post-65 medical  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 5.00%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Other postretirement benefit plans | Post-65 prescription  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 10.00%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Southern Company Gas [Member] | Other postretirement benefit plans | Pre-65  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 6.60%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2038
Southern Company Gas [Member] | Other postretirement benefit plans | Post-65 medical  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 8.40%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2038
Southern Company Gas [Member] | Other postretirement benefit plans | Post-65 prescription  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 8.40%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2038
Alabama Power [Member]  
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]  
Benefit obligation, 1 percent increase $ 28,000,000
Benefit obligation, 1 percent decrease 24,000,000
Service and interest costs, 1 percent increase 1,000,000
Service and interest costs, 1 percent decrease $ 1,000,000
Alabama Power [Member] | Other postretirement benefit plans | Pre-65  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 6.50%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Alabama Power [Member] | Other postretirement benefit plans | Post-65 medical  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 5.00%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Alabama Power [Member] | Other postretirement benefit plans | Post-65 prescription  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 10.00%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Georgia Power [Member]  
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]  
Benefit obligation, 1 percent increase $ 55,000,000
Benefit obligation, 1 percent decrease 48,000,000
Service and interest costs, 1 percent increase 2,000,000
Service and interest costs, 1 percent decrease $ 2,000,000
Georgia Power [Member] | Other postretirement benefit plans | Pre-65  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 6.50%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Georgia Power [Member] | Other postretirement benefit plans | Post-65 medical  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 5.00%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Georgia Power [Member] | Other postretirement benefit plans | Post-65 prescription  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 10.00%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Gulf Power [Member]  
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]  
Benefit obligation, 1 percent increase $ 4,000,000
Benefit obligation, 1 percent decrease 3,000,000
Service and interest costs, 1 percent increase 0
Service and interest costs, 1 percent decrease $ 0
Gulf Power [Member] | Other postretirement benefit plans | Pre-65  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 6.50%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Gulf Power [Member] | Other postretirement benefit plans | Post-65 medical  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 5.00%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Gulf Power [Member] | Other postretirement benefit plans | Post-65 prescription  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 10.00%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Mississippi Power [Member]  
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]  
Benefit obligation, 1 percent increase $ 5,000,000
Benefit obligation, 1 percent decrease 4,000,000
Service and interest costs, 1 percent increase 0
Service and interest costs, 1 percent decrease $ 0
Mississippi Power [Member] | Other postretirement benefit plans | Pre-65  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 6.50%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Mississippi Power [Member] | Other postretirement benefit plans | Post-65 medical  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 5.00%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Mississippi Power [Member] | Other postretirement benefit plans | Post-65 prescription  
Defined Benefit Plan Disclosure [Line Items]  
Initial Cost Trend Rate 10.00%
Ultimate Cost Trend Rate 4.50%
Year That Ultimate Rate Is Reached 2025
Successor [Member] | Southern Company Gas [Member]  
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]  
Benefit obligation, 1 percent increase $ 14,000,000
Benefit obligation, 1 percent decrease 12,000,000
Service and interest costs, 1 percent increase 0
Service and interest costs, 1 percent decrease $ 0