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Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Deferred tax liabilities -    
Deferred income tax liabilities $ 23,512 $ 18,945
Deferred tax assets -    
Deferred income tax assets 9,495 6,683
Valuation allowance (23) (4)
Total deferred tax liabilities, net 14,040 12,266
Accumulated deferred income taxes – assets 52 56
Accumulated deferred income taxes – liability 14,092 12,322
Accelerated depreciation [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 15,392 12,767
Property basis differences [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 2,708 1,603
Leveraged lease basis differences [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 314 308
Employee benefit obligations    
Deferred tax liabilities -    
Deferred income tax liabilities 737 579
Deferred tax assets -    
Deferred income tax assets 1,868 1,720
Premium on reacquired debt [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 89 95
Regulatory assets associated with employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 1,584 1,378
Regulatory assets associated with asset retirement obligations [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 1,781 1,422
Other deferred tax liabilities [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 907 793
Federal effect of state deferred taxes [Member]    
Deferred tax assets -    
Deferred income tax assets 597 479
Over recovered fuel clause [Member]    
Deferred tax assets -    
Deferred income tax assets 66 104
Other property basis differences [Member]    
Deferred tax assets -    
Deferred income tax assets 401 695
Deferred costs [Member]    
Deferred tax assets -    
Deferred income tax assets 100 83
Investment Tax Credit Carryforward [Member]    
Deferred tax assets -    
Deferred income tax assets 1,974 770
Federal NOL Carryforward [Member]    
Deferred tax assets -    
Deferred income tax assets 1,084 38
Unbilled revenues [Member]    
Deferred tax assets -    
Deferred income tax assets 92 111
Other Comprehensive Income Losses [Member]    
Deferred tax assets -    
Deferred income tax assets 152 85
Asset retirement obligations    
Deferred tax assets -    
Deferred income tax assets 1,732 1,482
Kemper IGCC Loss [Member]    
Deferred tax assets -    
Deferred income tax assets 484 451
Deferred State Tax Assets [Member]    
Deferred tax assets -    
Deferred income tax assets 266 222
Other deferred tax assets [Member]    
Deferred tax assets -    
Deferred income tax assets 679 443
Alabama Power [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 6,198 5,752
Deferred tax assets -    
Deferred income tax assets 1,544 1,511
Total deferred tax liabilities, net 4,654 4,241
Accumulated deferred income taxes – liability 4,654 4,241
Alabama Power [Member] | Accelerated depreciation [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 4,307 3,917
Alabama Power [Member] | Property basis differences [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 456 456
Alabama Power [Member] | Leveraged lease basis differences [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 26 28
Alabama Power [Member] | Employee benefit obligations    
Deferred tax liabilities -    
Deferred income tax liabilities 201 200
Deferred tax assets -    
Deferred income tax assets 427 407
Alabama Power [Member] | Regulatory assets associated with employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 393 375
Alabama Power [Member] | Regulatory assets associated with asset retirement obligations [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 347 312
Alabama Power [Member] | Other deferred tax liabilities [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 179 175
Alabama Power [Member] | Federal effect of state deferred taxes [Member]    
Deferred tax assets -    
Deferred income tax assets 266 242
Alabama Power [Member] | Unbilled revenues [Member]    
Deferred tax assets -    
Deferred income tax assets 36 39
Alabama Power [Member] | Other Comprehensive Income Losses [Member]    
Deferred tax assets -    
Deferred income tax assets 19 20
Alabama Power [Member] | Other deferred tax assets [Member]    
Deferred tax assets -    
Deferred income tax assets 139 180
Alabama Power [Member] | Asset retirement obligation [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 289 289
Deferred tax assets -    
Deferred income tax assets 636 600
Alabama Power [Member] | Storm damage reserves    
Deferred tax assets -    
Deferred income tax assets 21 23
Georgia Power [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 8,382 7,704
Deferred tax assets -    
Deferred income tax assets 2,382 2,077
Total deferred tax liabilities, net 6,000 5,627
Accumulated deferred income taxes – liability 6,000 5,627
Georgia Power [Member] | Accelerated depreciation [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 5,266 4,909
Georgia Power [Member] | Property basis differences [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 957 1,003
Georgia Power [Member] | Employee benefit obligations    
Deferred tax liabilities -    
Deferred income tax liabilities 428 310
Deferred tax assets -    
Deferred income tax assets 661 642
Georgia Power [Member] | Premium on reacquired debt [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 56 61
Georgia Power [Member] | Regulatory Assets Associated With Storm Damage Reserves [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 83 37
Georgia Power [Member] | Regulatory assets associated with employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 546 528
Georgia Power [Member] | Regulatory Assets Associated With Retired Assets [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 55 58
Georgia Power [Member] | Regulatory assets associated with asset retirement obligations [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 726 545
Georgia Power [Member] | Other deferred tax liabilities [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 83 92
Georgia Power [Member] | Federal effect of state deferred taxes [Member]    
Deferred tax assets -    
Deferred income tax assets 173 150
Georgia Power [Member] | Other property basis differences [Member]    
Deferred tax assets -    
Deferred income tax assets 105 88
Georgia Power [Member] | Deferred costs [Member]    
Deferred tax assets -    
Deferred income tax assets 100 83
Georgia Power [Member] | Unbilled revenues [Member]    
Deferred tax assets -    
Deferred income tax assets 47 47
Georgia Power [Member] | Regulatory Liabilities Associated With Asset Retirement Obligations [Member]    
Deferred tax assets -    
Deferred income tax assets 33 60
Georgia Power [Member] | Other deferred tax assets [Member]    
Deferred tax assets -    
Deferred income tax assets 70 82
Georgia Power [Member] | Asset retirement obligation [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 182 161
Deferred tax assets -    
Deferred income tax assets 908 706
Georgia Power [Member] | Tax credit carryforward [Member]    
Deferred tax assets -    
Deferred income tax assets 201 216
Georgia Power [Member] | Federal Tax Credit Carryforward [Member]    
Deferred tax assets -    
Deferred income tax assets 84 3
Gulf Power [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 1,192 1,109
Deferred tax assets -    
Deferred income tax assets 244 216
Total deferred tax liabilities, net 948 893
Accumulated deferred income taxes – liability 948 893
Gulf Power [Member] | Accelerated depreciation [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 834 812
Gulf Power [Member] | Property basis differences [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 123 133
Gulf Power [Member] | Employee benefit obligations    
Deferred tax liabilities -    
Deferred income tax liabilities 58 39
Gulf Power [Member] | Regulatory Assets [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 45 16
Gulf Power [Member] | Regulatory assets associated with employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 65 59
Gulf Power [Member] | Regulatory assets associated with asset retirement obligations [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 55 40
Gulf Power [Member] | Other deferred tax liabilities [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 12 10
Gulf Power [Member] | Federal effect of state deferred taxes [Member]    
Deferred tax assets -    
Deferred income tax assets 37 33
Gulf Power [Member] | Other deferred tax assets [Member]    
Deferred tax assets -    
Deferred income tax assets 19 19
Gulf Power [Member] | Pension and other employee benefits [Member]    
Deferred tax assets -    
Deferred income tax assets 72 65
Gulf Power [Member] | Asset retirement obligation [Member]    
Deferred tax assets -    
Deferred income tax assets 55 40
Gulf Power [Member] | Other postretirement benefit plans    
Deferred tax assets -    
Deferred income tax assets 26 26
Gulf Power [Member] | Tax credit carryforward [Member]    
Deferred tax assets -    
Deferred income tax assets 18 18
Gulf Power [Member] | Property damage reserves-liability    
Deferred tax assets -    
Deferred income tax assets 17 15
Mississippi Power [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 1,780 2,162
Deferred tax assets -    
Deferred income tax assets 1,024 1,400
Total deferred tax liabilities, net 756 762
Accumulated deferred income taxes – liability 756 762
Mississippi Power [Member] | Accelerated depreciation [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 386 1,618
Mississippi Power [Member] | Property basis differences [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 852 0
Deferred tax assets -    
Deferred income tax assets 0 451
Mississippi Power [Member] | Regulatory assets associated with employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 70 66
Mississippi Power [Member] | Regulatory assets associated with asset retirement obligations [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 72 71
Mississippi Power [Member] | Other deferred tax liabilities [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 125 176
Mississippi Power [Member] | Federal effect of state deferred taxes [Member]    
Deferred tax assets -    
Deferred income tax assets 19 8
Mississippi Power [Member] | Over recovered fuel clause [Member]    
Deferred tax assets -    
Deferred income tax assets 26 51
Mississippi Power [Member] | Kemper IGCC Loss [Member]    
Deferred tax assets -    
Deferred income tax assets 484 451
Mississippi Power [Member] | Other deferred tax assets [Member]    
Deferred tax assets -    
Deferred income tax assets 33 33
Mississippi Power [Member] | NOL State Carryforward [Member]    
Deferred tax assets -    
Deferred income tax assets 113 152
Mississippi Power [Member] | Deferred Federal Tax Assets [Member]    
Deferred tax assets -    
Deferred income tax assets 31 31
Mississippi Power [Member] | Pension and other employee benefits [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 49 30
Deferred tax assets -    
Deferred income tax assets 96 92
Mississippi Power [Member] | Federal NOL [Member]    
Deferred tax assets -    
Deferred income tax assets 109 17
Mississippi Power [Member] | Kemper IGCC    
Deferred tax liabilities -    
Deferred income tax liabilities 82 86
Mississippi Power [Member] | Asset retirement obligation [Member]    
Deferred tax assets -    
Deferred income tax assets 72 71
Mississippi Power [Member] | Rate Differential [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 144 115
Mississippi Power [Member] | Property insurance [Member]    
Deferred tax assets -    
Deferred income tax assets 27 25
Mississippi Power [Member] | Premium on long-term debt [Member]    
Deferred tax assets -    
Deferred income tax assets 14 18
Southern Power [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 2,495 1,393
Deferred tax assets -    
Deferred income tax assets 2,937 794
Valuation allowance 0 (2)
Total deferred tax liabilities, net   601
Net deferred income tax assets 2,937 792
Deferred tax assets, net 442  
Accumulated deferred income taxes – assets 594 0
Accumulated deferred income taxes – liability 152 601
Southern Power [Member] | Other deferred tax liabilities [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 27 7
Southern Power [Member] | Federal effect of state deferred taxes [Member]    
Deferred tax assets -    
Deferred income tax assets 53 40
Southern Power [Member] | Investment Tax Credit Carryforward [Member]    
Deferred tax assets -    
Deferred income tax assets 292 149
Southern Power [Member] | Deferred State Tax Assets [Member]    
Deferred tax assets -    
Deferred income tax assets 60 13
Southern Power [Member] | Other deferred tax assets [Member]    
Deferred tax assets -    
Deferred income tax assets 8 14
Southern Power [Member] | Accelerated depreciation and other property basis differences [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 2,440 1,364
Southern Power [Member] | Levelized capacity revenues [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 28 22
Southern Power [Member] | Tax credit carryforward [Member]    
Deferred tax assets -    
Deferred income tax assets 15 15
Southern Power [Member] | Unrealized Tax Credits [Member]    
Deferred tax assets -    
Deferred income tax assets 1,685 551
Southern Power [Member] | Federal Net Operating Loss [Member]    
Deferred tax assets -    
Deferred income tax assets 808 9
Southern Power [Member] | Investment In Partnerships [Member]    
Deferred tax assets -    
Deferred income tax assets 16 3
Successor [Member] | Southern Company Gas [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 2,554  
Deferred tax assets -    
Deferred income tax assets 598  
Valuation allowance (19)  
Total deferred tax liabilities, net 1,975  
Net deferred income tax assets 579  
Accumulated deferred income taxes – liability 1,975  
Successor [Member] | Southern Company Gas [Member] | Accelerated depreciation [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 1,954  
Successor [Member] | Southern Company Gas [Member] | Property basis differences [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 311  
Successor [Member] | Southern Company Gas [Member] | Employee benefit obligations    
Deferred tax assets -    
Deferred income tax assets 165  
Successor [Member] | Southern Company Gas [Member] | Regulatory assets associated with employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 125  
Successor [Member] | Southern Company Gas [Member] | Other deferred tax liabilities [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities 164  
Successor [Member] | Southern Company Gas [Member] | Federal effect of state deferred taxes [Member]    
Deferred tax assets -    
Deferred income tax assets 42  
Successor [Member] | Southern Company Gas [Member] | Other deferred tax assets [Member]    
Deferred tax assets -    
Deferred income tax assets 332  
Successor [Member] | Southern Company Gas [Member] | Federal NOL [Member]    
Deferred tax assets -    
Deferred income tax assets $ 59  
Predecessor [Member] | Southern Company Gas [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities   2,362
Deferred tax assets -    
Deferred income tax assets   438
Valuation allowance   (19)
Total deferred tax liabilities, net   1,943
Net deferred income tax assets   419
Accumulated deferred income taxes – liability   1,912
Predecessor [Member] | Southern Company Gas [Member] | Accelerated depreciation [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities   1,820
Predecessor [Member] | Southern Company Gas [Member] | Property basis differences [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities   283
Predecessor [Member] | Southern Company Gas [Member] | Employee benefit obligations    
Deferred tax assets -    
Deferred income tax assets   164
Predecessor [Member] | Southern Company Gas [Member] | Regulatory assets associated with employee benefit obligations [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities   44
Predecessor [Member] | Southern Company Gas [Member] | Other deferred tax liabilities [Member]    
Deferred tax liabilities -    
Deferred income tax liabilities   215
Predecessor [Member] | Southern Company Gas [Member] | Federal effect of state deferred taxes [Member]    
Deferred tax assets -    
Deferred income tax assets   62
Predecessor [Member] | Southern Company Gas [Member] | Other deferred tax assets [Member]    
Deferred tax assets -    
Deferred income tax assets   212
Predecessor [Member] | Southern Company Gas [Member] | Federal NOL [Member]    
Deferred tax assets -    
Deferred income tax assets   $ 0