Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Assets:
Asset Derivatives	$ 29	$ 21
Liabilities:
Liability Derivatives	250	225
Fair Value, Measurements, Recurring [Member]
Assets:
Interest Rate Derivative Assets, at Fair Value	22	8
Nuclear decommissioning trusts:
Cash equivalents	790	397
Other investments	10	10
Fair value assets, total	2,338	1,971
Liabilities:
Liability Derivatives	250
Interest rate derivatives		24
Fair value liabilities, total		225
Fair Value, Measurements, Recurring [Member] | Domestic Equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	610	668
Fair Value, Measurements, Recurring [Member] | Foreign equity fund [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	207	218
Fair Value, Measurements, Recurring [Member] | U.S. Treasury and government agency securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	152	130
Fair Value, Measurements, Recurring [Member] | Municipal bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	64	62
Fair Value, Measurements, Recurring [Member] | Corporate bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	289	299
Fair Value, Measurements, Recurring [Member] | Mortgage and asset backed securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	145	139
Fair Value, Measurements, Recurring [Member] | Private equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	17	3
Fair Value, Measurements, Recurring [Member] | Other investments [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	25	24
Fair Value, Measurements, Recurring [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives	7	13
Liabilities:
Liability Derivatives	220	201
Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member]
Liabilities:
Liability Derivatives	30
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Interest Rate Derivative Assets, at Fair Value	0	0
Nuclear decommissioning trusts:
Cash equivalents	790	397
Other investments	9	9
Fair value assets, total	1,414	1,034
Liabilities:
Liability Derivatives	0
Interest rate derivatives		0
Fair value liabilities, total		0
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Domestic Equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	541	583
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Foreign equity fund [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	47	34
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury and government agency securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Municipal bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	11	0
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage and asset backed securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Private equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other investments [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	16	11
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives	0	0
Liabilities:
Liability Derivatives	0	0
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Interest Rate Contract [Member]
Liabilities:
Liability Derivatives	0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Interest Rate Derivative Assets, at Fair Value	22	8
Nuclear decommissioning trusts:
Cash equivalents	0	0
Other investments	0	0
Fair value assets, total	906	933
Liabilities:
Liability Derivatives	250
Interest rate derivatives		24
Fair value liabilities, total		225
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Domestic Equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	69	85
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Foreign equity fund [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	160	184
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury and government agency securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	152	130
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Municipal bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	64	62
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	278	299
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Mortgage and asset backed securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	145	139
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Private equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other investments [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	9	13
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives	7	13
Liabilities:
Liability Derivatives	220	201
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Contract [Member]
Liabilities:
Liability Derivatives	30
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Interest Rate Derivative Assets, at Fair Value	0	0
Nuclear decommissioning trusts:
Cash equivalents	0	0
Other investments	1	1
Fair value assets, total	1	1
Liabilities:
Liability Derivatives	0
Interest rate derivatives		0
Fair value liabilities, total		0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Domestic Equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Foreign equity fund [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury and government agency securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Municipal bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Mortgage and asset backed securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Private equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other investments [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives	0	0
Liabilities:
Liability Derivatives	0	0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Interest Rate Contract [Member]
Liabilities:
Liability Derivatives	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Net Asset Value As A Practical Expedient [Member]
Nuclear decommissioning trusts:
Fair value assets, total	17	3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Net Asset Value As A Practical Expedient [Member] | Private equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	17	3
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member]
Nuclear decommissioning trusts:
Cash equivalents	18	18
Fair value assets, total	19
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	1
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member] | Energy Related Derivative [Member]
Liabilities:
Liability Derivatives	100	72
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Nuclear decommissioning trusts:
Cash equivalents	18	18
Fair value assets, total	18
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Interest Rate Contract [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Energy Related Derivative [Member]
Liabilities:
Liability Derivatives	0	0
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Nuclear decommissioning trusts:
Cash equivalents	0	0
Fair value assets, total	1
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Contract [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	1
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Energy Related Derivative [Member]
Liabilities:
Liability Derivatives	100	72
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Nuclear decommissioning trusts:
Cash equivalents	0	0
Fair value assets, total	0
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Interest Rate Contract [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Energy Related Derivative [Member]
Liabilities:
Liability Derivatives	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member]
Nuclear decommissioning trusts:
Cash equivalents	63	802
Fair value assets, total	845
Liabilities:
Liability Derivatives	21	41
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Domestic Equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	183	182
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Foreign equity fund [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	113	121
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasury and government agency securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	125	96
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Municipal bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	64	62
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Corporate bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	143	188
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage and asset backed securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	127	121
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Other investments [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	20	19
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	5	6
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives	2	7
Liabilities:
Liability Derivatives	15	27
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member]
Liabilities:
Liability Derivatives	6	14
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Nuclear decommissioning trusts:
Cash equivalents	63	191
Fair value assets, total	261
Liabilities:
Liability Derivatives	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Domestic Equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	182	180
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Foreign equity fund [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury and government agency securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Municipal bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage and asset backed securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other investments [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	16	11
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Interest Rate Contract [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives	0	0
Liabilities:
Liability Derivatives	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Interest Rate Contract [Member]
Liabilities:
Liability Derivatives	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Nuclear decommissioning trusts:
Cash equivalents	0	611
Fair value assets, total	584
Liabilities:
Liability Derivatives	21	41
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Domestic Equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	1	2
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Foreign equity fund [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	113	121
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury and government agency securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	125	96
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Municipal bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	64	62
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	143	188
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Mortgage and asset backed securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	127	121
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other investments [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	4	8
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Contract [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	5	6
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives	2	7
Liabilities:
Liability Derivatives	15	27
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Contract [Member]
Liabilities:
Liability Derivatives	6	14
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Nuclear decommissioning trusts:
Cash equivalents	0	0
Fair value assets, total	0
Liabilities:
Liability Derivatives	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Domestic Equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Foreign equity fund [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury and government agency securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Municipal bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Mortgage and asset backed securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other investments [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Interest Rate Contract [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives	0	0
Liabilities:
Liability Derivatives	0	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Interest Rate Contract [Member]
Liabilities:
Liability Derivatives	0	0
Alabama Power [Member]
Assets:
Asset Derivatives	1	1
Liabilities:
Liability Derivatives	70	61
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member]
Nuclear decommissioning trusts:
Cash equivalents	68	162
Fair value assets, total	803	917
Liabilities:
Liability Derivatives	70	61
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Domestic Equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	427	486
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Foreign equity fund [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	94	97
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasury and government agency securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	27	34
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Corporate bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	146	111
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage and asset backed securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	18	18
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Private equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	17	3
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Other investments [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	5	5
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives	1	1
Liabilities:
Liability Derivatives	55	53
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member]
Liabilities:
Liability Derivatives	15	8
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Nuclear decommissioning trusts:
Cash equivalents	68	162
Fair value assets, total	485	599
Liabilities:
Liability Derivatives	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Domestic Equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	359	403
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Foreign equity fund [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	47	34
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury and government agency securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	11	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage and asset backed securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Private equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other investments [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives	0	0
Liabilities:
Liability Derivatives	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Interest Rate Contract [Member]
Liabilities:
Liability Derivatives	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Nuclear decommissioning trusts:
Cash equivalents	0	0
Fair value assets, total	301	315
Liabilities:
Liability Derivatives	70	61
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Domestic Equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	68	83
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Foreign equity fund [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	47	63
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury and government agency securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	27	34
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	135	111
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Mortgage and asset backed securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	18	18
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Private equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other investments [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	5	5
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives	1	1
Liabilities:
Liability Derivatives	55	53
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Contract [Member]
Liabilities:
Liability Derivatives	15	8
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Nuclear decommissioning trusts:
Cash equivalents	0	0
Fair value assets, total	0	0
Liabilities:
Liability Derivatives	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Domestic Equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Foreign equity fund [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury and government agency securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate bonds [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Mortgage and asset backed securities [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Private equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other investments [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives	0	0
Liabilities:
Liability Derivatives	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Interest Rate Contract [Member]
Liabilities:
Liability Derivatives	0	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Net Asset Value As A Practical Expedient [Member]
Nuclear decommissioning trusts:
Fair value assets, total	17	3
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Net Asset Value As A Practical Expedient [Member] | Private equity [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	17	3
Mississippi Power [Member] | Fair Value, Measurements, Recurring [Member]
Nuclear decommissioning trusts:
Cash equivalents	52	115
Mississippi Power [Member] | Fair Value, Measurements, Recurring [Member] | Energy Related Derivative [Member]
Liabilities:
Liability Derivatives	47	45
Mississippi Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Nuclear decommissioning trusts:
Cash equivalents	52	115
Mississippi Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Energy Related Derivative [Member]
Liabilities:
Liability Derivatives	0	0
Mississippi Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Nuclear decommissioning trusts:
Cash equivalents	0	0
Mississippi Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Energy Related Derivative [Member]
Liabilities:
Liability Derivatives	47	45
Mississippi Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Nuclear decommissioning trusts:
Cash equivalents	0	0
Mississippi Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Energy Related Derivative [Member]
Liabilities:
Liability Derivatives	0	0
Southern Power [Member]
Assets:
Asset Derivatives	7	5
Liabilities:
Liability Derivatives	3	4
Southern Power [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Asset Derivatives	4
Nuclear decommissioning trusts:
Cash equivalents	511	18
Fair value assets, total	518	23
Liabilities:
Liability Derivatives	3
Southern Power [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	3
Southern Power [Member] | Fair Value, Measurements, Recurring [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives		5
Liabilities:
Liability Derivatives		4
Southern Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Asset Derivatives	0
Nuclear decommissioning trusts:
Cash equivalents	511	18
Fair value assets, total	511	18
Liabilities:
Liability Derivatives	0
Southern Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Interest Rate Contract [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0
Southern Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives		0
Liabilities:
Liability Derivatives		0
Southern Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Asset Derivatives	4
Nuclear decommissioning trusts:
Cash equivalents	0	0
Fair value assets, total	7	5
Liabilities:
Liability Derivatives	3
Southern Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Contract [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	3
Southern Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives		5
Liabilities:
Liability Derivatives		4
Southern Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Asset Derivatives	0
Nuclear decommissioning trusts:
Cash equivalents	0	0
Fair value assets, total	0	0
Liabilities:
Liability Derivatives	0
Southern Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Interest Rate Contract [Member]
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	$ 0
Southern Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Energy Related Derivative [Member]
Assets:
Asset Derivatives		0
Liabilities:
Liability Derivatives		$ 0