Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities:
Consolidated net income	$ 2,300,000,000	$ 926,000,000	$ 2,529,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	3,549,000,000	3,457,000,000	2,923,000,000
Deferred income taxes	94,000,000	166,000,000	(127,000,000)
Amortization of investment tax credits	(87,000,000)	(79,000,000)	(59,000,000)
Collateral deposits	17,000,000	(4,000,000)	(102,000,000)
Allowance for equity funds used during construction	(138,000,000)	(160,000,000)	(202,000,000)
Pension and postretirement funding	(4,000,000)	(2,000,000)	(1,029,000,000)
Settlement of asset retirement obligations	(244,000,000)	(177,000,000)	(171,000,000)
Stock based compensation expense	125,000,000	109,000,000	121,000,000
Hedge settlements	(10,000,000)	6,000,000	(233,000,000)
Estimated loss on plants under construction	1,093,000,000	3,179,000,000	428,000,000
Impairment charges	210,000,000	0	0
Goodwill impairment	42,000,000
Gain on dispositions, net	(301,000,000)	(42,000,000)	(2,000,000)
Other, net	(22,000,000)	(112,000,000)	(219,000,000)
Changes in certain current assets and liabilities —
-Receivables	(426,000,000)	(202,000,000)	(544,000,000)
-Fossil fuel for generation	123,000,000	36,000,000	178,000,000
-Natural gas for sale	49,000,000	36,000,000	(226,000,000)
-Other current assets	(127,000,000)	(143,000,000)	(206,000,000)
-Accounts payable	291,000,000	(280,000,000)	301,000,000
-Accrued taxes	267,000,000	(142,000,000)	1,456,000,000
-Retail fuel cost over recovery	36,000,000	(212,000,000)	(231,000,000)
-Other current liabilities	63,000,000	(45,000,000)	250,000,000
Net cash provided from operating activities	6,945,000,000	6,394,000,000	4,894,000,000
Investing Activities:
Business acquisitions, net of cash acquired	(65,000,000)	(1,054,000,000)	(10,680,000,000)
Property additions	(8,001,000,000)	(7,423,000,000)	(7,310,000,000)
Proceeds pursuant to the Toshiba Guarantee, net of joint owner portion	0	1,682,000,000	0
Nuclear decommissioning trust fund purchases	(1,117,000,000)	(811,000,000)	(1,160,000,000)
Nuclear decommissioning trust fund sales	1,111,000,000	805,000,000	1,154,000,000
Proceeds from dispositions	2,956,000,000	97,000,000	15,000,000
Cost of removal, net of salvage	(388,000,000)	(313,000,000)	(245,000,000)
Change in construction payables, net	50,000,000	259,000,000	(121,000,000)
Investment in unconsolidated subsidiaries	(114,000,000)	(152,000,000)	(1,444,000,000)
Payments pursuant to LTSAs	(186,000,000)	(227,000,000)	(134,000,000)
Other investing activities	(6,000,000)	(53,000,000)	(122,000,000)
Net cash used for investing activities	(5,760,000,000)	(7,190,000,000)	(20,047,000,000)
Financing Activities:
Increase (decrease) in notes payable, net	(774,000,000)	(401,000,000)	1,228,000,000
Proceeds —
Long-term debt	2,478,000,000	5,858,000,000	16,368,000,000
Common stock	1,090,000,000	793,000,000	3,758,000,000
Preferred stock	0	250,000,000	0
Short-term borrowings	3,150,000,000	1,259,000,000	0
Redemptions and repurchases —
Long-term debt	(5,533,000,000)	(2,930,000,000)	(3,145,000,000)
Preferred and preference stock	(33,000,000)	(658,000,000)	0
Short-term borrowings	(1,900,000,000)	(659,000,000)	(478,000,000)
Other long-term debt	(100,000,000)	0	0
Distributions to noncontrolling interests	(153,000,000)	(119,000,000)	(72,000,000)
Capital contributions from noncontrolling interests	2,551,000,000	80,000,000	682,000,000
Payment of common stock dividends	(2,425,000,000)	(2,300,000,000)	(2,104,000,000)
Other financing activities	(264,000,000)	(222,000,000)	(512,000,000)
Net cash provided from (used for) financing activities	(1,813,000,000)	951,000,000	15,725,000,000
Net Change in Cash, Cash Equivalents, and Restricted Cash	(628,000,000)	155,000,000	572,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	2,147,000,000	1,992,000,000	1,420,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	1,519,000,000	2,147,000,000	1,992,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	1,794,000,000	1,676,000,000	1,066,000,000
Income taxes (net of refunds)	172,000,000	(410,000,000)	(148,000,000)
Noncash transactions —
Accrued property additions at year-end	1,103,000,000	985,000,000	1,262,000,000
Alabama Power
Operating Activities:
Consolidated net income	945,000,000	866,000,000	839,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	917,000,000	888,000,000	844,000,000
Deferred income taxes	174,000,000	409,000,000	407,000,000
Allowance for equity funds used during construction	(62,000,000)	(39,000,000)	(28,000,000)
Pension and postretirement funding	(4,000,000)	(2,000,000)	(133,000,000)
Settlement of asset retirement obligations	(55,000,000)	(26,000,000)	(25,000,000)
Other, net	(1,000,000)	13,000,000	(77,000,000)
Changes in certain current assets and liabilities —
-Receivables	(149,000,000)	(168,000,000)	94,000,000
-Prepayments	(2,000,000)	(2,000,000)	1,000,000
-Other current assets	30,000,000	20,000,000	38,000,000
-Accounts payable	24,000,000	71,000,000	73,000,000
-Accrued taxes	10,000,000	(84,000,000)	93,000,000
-Retail fuel cost over recovery	0	(76,000,000)	(162,000,000)
-Other current liabilities	128,000,000	3,000,000	11,000,000
-Materials and supplies	(82,000,000)	(34,000,000)	(38,000,000)
-Accrued compensation	8,000,000	(2,000,000)	12,000,000
Net cash provided from operating activities	1,881,000,000	1,837,000,000	1,949,000,000
Investing Activities:
Property additions	(2,158,000,000)	(1,882,000,000)	(1,272,000,000)
Nuclear decommissioning trust fund purchases	(279,000,000)	(237,000,000)	(352,000,000)
Nuclear decommissioning trust fund sales	278,000,000	237,000,000	351,000,000
Cost of removal, net of salvage	(130,000,000)	(112,000,000)	(94,000,000)
Change in construction payables, net	26,000,000	161,000,000	(37,000,000)
Other investing activities	(26,000,000)	(43,000,000)	(34,000,000)
Net cash used for investing activities	(2,289,000,000)	(1,876,000,000)	(1,438,000,000)
Proceeds —
Preferred stock	0	250,000,000	0
Senior notes	500,000,000	1,100,000,000	400,000,000
Pollution control revenue bonds	120,000,000	0	0
Other long-term debt	0	0	45,000,000
Capital contributions from parent company	511,000,000	361,000,000	260,000,000
Redemptions and repurchases —
Preferred and preference stock	0	(238,000,000)	0
Senior notes	0	(525,000,000)	(200,000,000)
Pollution control revenue bonds	(120,000,000)	(36,000,000)	0
Payment of common stock dividends	(801,000,000)	(714,000,000)	(765,000,000)
Other financing activities	(33,000,000)	(35,000,000)	(25,000,000)
Net cash provided from (used for) financing activities	177,000,000	163,000,000	(285,000,000)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(231,000,000)	124,000,000	226,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	544,000,000	420,000,000	194,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	313,000,000	544,000,000	420,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	284,000,000	285,000,000	277,000,000
Income taxes (net of refunds)	106,000,000	236,000,000	(108,000,000)
Noncash transactions —
Accrued property additions at year-end	272,000,000	245,000,000	84,000,000
Georgia Power
Operating Activities:
Consolidated net income	793,000,000	1,428,000,000	1,347,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	1,142,000,000	1,100,000,000	1,063,000,000
Deferred income taxes	(260,000,000)	458,000,000	383,000,000
Pension, postretirement, and other employee benefits	(75,000,000)	(68,000,000)	(33,000,000)
Pension and postretirement funding	0	0	(287,000,000)
Settlement of asset retirement obligations	(116,000,000)	(120,000,000)	(123,000,000)
Other deferred charges — affiliated	0	0	(111,000,000)
Estimated loss on plants under construction	1,060,000,000	0	0
Other, net	(21,000,000)	(83,000,000)	(25,000,000)
Changes in certain current assets and liabilities —
-Receivables	8,000,000	(256,000,000)	60,000,000
-Fossil fuel for generation	83,000,000	(16,000,000)	104,000,000
-Other current assets	(43,000,000)	(28,000,000)	(38,000,000)
-Accounts payable	95,000,000	(219,000,000)	(42,000,000)
-Accrued taxes	58,000,000	1,000,000	131,000,000
-Retail fuel cost over recovery	0	(84,000,000)	(32,000,000)
-Other current liabilities	(107,000,000)	(33,000,000)	28,000,000
-Prepaid income taxes	152,000,000	(168,000,000)	0
Net cash provided from operating activities	2,769,000,000	1,912,000,000	2,425,000,000
Investing Activities:
Property additions	(3,116,000,000)	(2,704,000,000)	(2,223,000,000)
Proceeds pursuant to the Toshiba Guarantee, net of joint owner portion	0	1,682,000,000	0
Nuclear decommissioning trust fund purchases	(839,000,000)	(574,000,000)	(808,000,000)
Nuclear decommissioning trust fund sales	833,000,000	568,000,000	803,000,000
Cost of removal, net of salvage	(107,000,000)	(100,000,000)	(83,000,000)
Payments pursuant to LTSAs	(54,000,000)	(64,000,000)	(34,000,000)
Change in construction payables, net of joint owner portion	68,000,000	223,000,000	(35,000,000)
Proceeds from asset dispositions	138,000,000	96,000,000	10,000,000
Other investing activities	(32,000,000)	(39,000,000)	23,000,000
Net cash used for investing activities	(3,109,000,000)	(912,000,000)	(2,347,000,000)
Financing Activities:
Increase (decrease) in notes payable, net	294,000,000	(391,000,000)	234,000,000
Proceeds —
Short-term borrowings	0	700,000,000	0
Senior notes	0	1,350,000,000	650,000,000
Pollution control revenue bonds	108,000,000	65,000,000	0
Other long-term debt	0	370,000,000	0
Capital contributions from parent company	2,985,000,000	431,000,000	594,000,000
FFB loan	0	0	425,000,000
Redemptions and repurchases —
Preferred and preference stock	0	(270,000,000)	0
Short-term borrowings	(150,000,000)	(550,000,000)	0
Senior notes	(1,500,000,000)	(450,000,000)	(700,000,000)
Pollution control revenue bonds	(469,000,000)	(65,000,000)	(4,000,000)
Payment of common stock dividends	(1,396,000,000)	(1,281,000,000)	(1,305,000,000)
Premiums on redemption and repurchases of senior notes	(152,000,000)	0	0
Other financing activities	(20,000,000)	(60,000,000)	(36,000,000)
Net cash provided from (used for) financing activities	(400,000,000)	(151,000,000)	(142,000,000)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(740,000,000)	849,000,000	(64,000,000)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	852,000,000	3,000,000	67,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	112,000,000	852,000,000	3,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	408,000,000	386,000,000	375,000,000
Income taxes (net of refunds)	300,000,000	496,000,000	170,000,000
Noncash transactions —
Accrued property additions at year-end	683,000,000	550,000,000	336,000,000
Mississippi Power
Operating Activities:
Consolidated net income	236,000,000	(2,588,000,000)	(48,000,000)
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	177,000,000	198,000,000	157,000,000
Deferred income taxes	475,000,000	(727,000,000)	(67,000,000)
Allowance for equity funds used during construction	0	(72,000,000)	(124,000,000)
Pension and postretirement funding	0	0	(47,000,000)
Settlement of asset retirement obligations	(35,000,000)	(23,000,000)	(23,000,000)
Estimated loss on plants under construction	33,000,000	3,179,000,000	428,000,000
Other, net	18,000,000	(8,000,000)	(9,000,000)
Changes in certain current assets and liabilities —
-Receivables	(19,000,000)	540,000,000	13,000,000
-Fossil fuel for generation	(3,000,000)	24,000,000	4,000,000
-Other current assets	(7,000,000)	(13,000,000)	(12,000,000)
-Accounts payable	15,000,000	(3,000,000)	(14,000,000)
-Accrued taxes	(46,000,000)	80,000,000	14,000,000
-Other current liabilities	(41,000,000)	(3,000,000)	9,000,000
-Prepaid income taxes	(12,000,000)	0	39,000,000
-Accrued interest	(1,000,000)	(29,000,000)	27,000,000
-Over recovered regulatory clause revenues	14,000,000	(51,000,000)	(45,000,000)
-Customer liability associated with Kemper refunds	0	(1,000,000)	(73,000,000)
Net cash provided from operating activities	804,000,000	503,000,000	229,000,000
Investing Activities:
Property additions	(188,000,000)	(429,000,000)	(798,000,000)
Change in construction payables, net	4,000,000	(47,000,000)	(26,000,000)
Payments pursuant to LTSAs	(29,000,000)	(10,000,000)	10,000,000
Government grant proceeds	0	0	137,000,000
Other investing activities	(19,000,000)	(18,000,000)	(20,000,000)
Net cash used for investing activities	(232,000,000)	(504,000,000)	(697,000,000)
Financing Activities:
Increase (decrease) in notes payable, net	(4,000,000)	(18,000,000)	0
Proceeds —
Short-term borrowings	300,000,000	109,000,000	0
Senior notes	600,000,000	0	0
Other long-term debt	0	0	1,200,000,000
Capital contributions from parent company	15,000,000	1,002,000,000	627,000,000
Long-term debt issuance to parent company	0	40,000,000	200,000,000
Redemptions and repurchases —
Preferred and preference stock	(33,000,000)	0	0
Short-term borrowings	(300,000,000)	(109,000,000)	(478,000,000)
Senior notes	(155,000,000)	(35,000,000)	(300,000,000)
Pollution control revenue bonds	(43,000,000)	0	0
Long-term debt to parent company	0	(591,000,000)	(225,000,000)
Capital leases	0	(71,000,000)	(3,000,000)
Other long-term debt	(900,000,000)	(300,000,000)	(425,000,000)
Other financing activities	(7,000,000)	(2,000,000)	(2,000,000)
Net cash provided from (used for) financing activities	(527,000,000)	25,000,000	594,000,000
Net Change in Cash, Cash Equivalents, and Restricted Cash	45,000,000	24,000,000	126,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	248,000,000	224,000,000	98,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	293,000,000	248,000,000	224,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	80,000,000	65,000,000	50,000,000
Income taxes (net of refunds)	(525,000,000)	(424,000,000)	(97,000,000)
Noncash transactions —
Accrued property additions at year-end	35,000,000	32,000,000	78,000,000
Southern Power
Operating Activities:
Consolidated net income	246,000,000	1,117,000,000	374,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	524,000,000	536,000,000	370,000,000
Deferred income taxes	(239,000,000)	(263,000,000)	(1,063,000,000)
Amortization of investment tax credits	(58,000,000)	(57,000,000)	(37,000,000)
Collateral deposits	17,000,000	(4,000,000)	(102,000,000)
Income taxes receivable, non-current	42,000,000	(61,000,000)	(13,000,000)
Impairment charges	156,000,000	0	0
Gain on dispositions, net	2,000,000	0	0
Accrued income taxes, non-current	(14,000,000)	14,000,000	(109,000,000)
Other, net	(10,000,000)	(9,000,000)	12,000,000
Changes in certain current assets and liabilities —
-Receivables	(20,000,000)	(60,000,000)	(54,000,000)
-Other current assets	(26,000,000)	(28,000,000)	4,000,000
-Accrued taxes	7,000,000	(55,000,000)	940,000,000
-Other current liabilities	(19,000,000)	1,000,000	46,000,000
-Prepaid income taxes	25,000,000	24,000,000	(29,000,000)
Net cash provided from operating activities	631,000,000	1,155,000,000	339,000,000
Investing Activities:
Business acquisitions, net of cash acquired	(65,000,000)	(1,016,000,000)	(2,284,000,000)
Property additions	(315,000,000)	(268,000,000)	(2,114,000,000)
Proceeds from dispositions	203,000,000	0	0
Change in construction payables, net of joint owner portion	(6,000,000)	(153,000,000)	(57,000,000)
Payments pursuant to LTSAs and for equipment not yet received	(75,000,000)	(203,000,000)	(350,000,000)
Other investing activities	31,000,000	15,000,000	16,000,000
Net cash used for investing activities	(227,000,000)	(1,625,000,000)	(4,789,000,000)
Financing Activities:
Increase (decrease) in notes payable, net	(105,000,000)	(104,000,000)	73,000,000
Proceeds —
Short-term borrowings	200,000,000	0	0
Senior notes	0	525,000,000	2,831,000,000
Other long-term debt	0	43,000,000	65,000,000
Capital contributions from parent company	2,000,000	0	1,850,000,000
Redemptions and repurchases —
Short-term borrowings	(100,000,000)	0	0
Senior notes	(350,000,000)	(500,000,000)	(200,000,000)
Other long-term debt	(420,000,000)	(18,000,000)	(86,000,000)
Return of capital	(1,650,000,000)	0	0
Distributions to noncontrolling interests	(153,000,000)	(119,000,000)	(57,000,000)
Capital contributions from noncontrolling interests	2,551,000,000	80,000,000	682,000,000
Purchase of membership interests from noncontrolling interests	0	(59,000,000)	(129,000,000)
Payment of common stock dividends	(312,000,000)	(317,000,000)	(272,000,000)
Other financing activities	(26,000,000)	(33,000,000)	(30,000,000)
Net cash provided from (used for) financing activities	(363,000,000)	(502,000,000)	4,727,000,000
Net Change in Cash, Cash Equivalents, and Restricted Cash	41,000,000	(972,000,000)	277,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	140,000,000	1,112,000,000	835,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	181,000,000	140,000,000	1,112,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	173,000,000	189,000,000	89,000,000
Income taxes (net of refunds)	79,000,000	(487,000,000)	116,000,000
Noncash transactions —
Accrued property additions at year-end	31,000,000	32,000,000	251,000,000
Accrued acquisitions at year-end	0	0	461,000,000
Southern Company Gas
Operating Activities:
Consolidated net income	372,000,000	243,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	500,000,000	501,000,000
Deferred income taxes	(1,000,000)	236,000,000
Pension and postretirement funding	0	0
Hedge settlements	0	0
Goodwill impairment	42,000,000	0
Gain on dispositions, net	(291,000,000)	0
Mark-to-market adjustments	(19,000,000)	(24,000,000)
Other, net	(24,000,000)	(51,000,000)
Changes in certain current assets and liabilities —
-Receivables	(218,000,000)	(94,000,000)
-Natural gas for sale	49,000,000	36,000,000
-Other current assets	4,000,000	(24,000,000)
-Accounts payable	372,000,000	(20,000,000)
-Accrued taxes	10,000,000	110,000,000
-Other current liabilities	(22,000,000)	(8,000,000)
-Prepaid income taxes	(42,000,000)	(39,000,000)
-Accrued compensation	32,000,000	15,000,000
Net cash provided from operating activities	764,000,000	881,000,000
Investing Activities:
Property additions	(1,388,000,000)	(1,514,000,000)
Proceeds from dispositions	2,609,000,000	0
Cost of removal, net of salvage	(96,000,000)	(66,000,000)
Change in construction payables, net	(37,000,000)	72,000,000
Investment in unconsolidated subsidiaries	(110,000,000)	(145,000,000)
Returned investment in unconsolidated subsidiaries	20,000,000	80,000,000
Other investing activities	0	5,000,000
Net cash used for investing activities	998,000,000	(1,568,000,000)
Financing Activities:
Increase (decrease) in notes payable, net	(868,000,000)	262,000,000
Proceeds —
First mortgage bonds	300,000,000	400,000,000
Senior notes	0	450,000,000
Capital contributions from parent company	24,000,000	103,000,000
Redemptions and repurchases —
Gas facility revenue bonds	(200,000,000)	0
Medium-term notes	0	(22,000,000)
Senior notes	(155,000,000)	0
First mortgage bonds	0	0
Return of capital	(400,000,000)	0
Distributions to noncontrolling interests	0	0
Purchase of 15% noncontrolling interest in SouthStar	0	0
Payment of common stock dividends	(468,000,000)	(443,000,000)
Other financing activities	(3,000,000)	(9,000,000)
Net cash provided from (used for) financing activities	(1,770,000,000)	741,000,000
Net Change in Cash, Cash Equivalents, and Restricted Cash	(8,000,000)	54,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	78,000,000	24,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	70,000,000	78,000,000	24,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	249,000,000	223,000,000
Income taxes (net of refunds)	524,000,000	72,000,000
Noncash transactions —
Accrued property additions at year-end	$ 97,000,000	$ 135,000,000
Predecessor | Southern Company Gas
Redemptions and repurchases —
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year			$ 22,000,000