Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating Activities:
Net income	$ 936	$ 665
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	873	823
Deferred income taxes	34	161
Allowance for equity funds used during construction	(30)	(57)
Stock based compensation expense	69	61
Estimated loss on Kemper IGCC	37	108
Mark-to-market adjustments	(60)	(81)
Other, net	6	(10)
Changes in certain current assets and liabilities —
-Receivables	197	310
-Prepayments	(82)	(111)
-Natural gas for sale, net of temporary LIFO liquidation	413	411
-Other current assets	7	(31)
-Accounts payable	(425)	(533)
-Accrued taxes	(79)	(212)
-Accrued compensation	(471)	(438)
-Retail fuel cost over recovery	3	(122)
-Other current liabilities	81	(48)
Net cash provided from operating activities	1,509	896
Investing Activities:
Business acquisitions, net of cash acquired	(46)	(1,004)
Property additions	(1,781)	(1,488)
Nuclear decommissioning trust fund purchases	(306)	(224)
Nuclear decommissioning trust fund sales	301	218
Cost of removal, net of salvage	(79)	(61)
Change in construction payables, net	(112)	(170)
Investment in unconsolidated subsidiaries	(30)	(81)
Payments pursuant to LTSAs	(73)	(55)
Asset dispositions	135	64
Other investing activities	(4)	4
Net cash used for investing activities	(1,995)	(2,797)
Financing Activities:
Increase (decrease) in notes payable, net	782	573
Proceeds —
Long-term debt	600	1,409
Common stock	113	186
Short-term borrowings	1,200	4
Redemptions and repurchases —
Long-term debt	(1,283)	(608)
Short-term borrowings	(150)	0
Distributions to noncontrolling interests	(13)	(18)
Capital contributions from noncontrolling interests	8	71
Payment of common stock dividends	(586)	(556)
Other financing activities	(42)	(36)
Net cash provided from financing activities	629	1,025
Net Change in Cash, Cash Equivalents, and Restricted Cash	143	(876)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	2,147	1,992
Cash, Cash Equivalents, and Restricted Cash at End of Period	2,290	1,116
Cash paid (received) during the period for —
Interest	499	461
Income taxes, net	(1)	(6)
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	894	578
ALABAMA POWER CO
Operating Activities:
Net income	229	178
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	228	219
Deferred income taxes	32	59
Allowance for equity funds used during construction	(13)	(8)
Other, net	(22)	(3)
Changes in certain current assets and liabilities —
-Prepayments	(82)	(76)
-Materials and supplies	27	10
-Other current assets	19	39
-Accounts payable	(216)	(214)
-Accrued taxes	57	77
-Accrued compensation	(108)	(96)
-Retail fuel cost over recovery		(36)
-Other current liabilities	45	(9)
Net cash provided from operating activities	155	128
Investing Activities:
Property additions	(490)	(306)
Nuclear decommissioning trust fund purchases	(50)	(63)
Nuclear decommissioning trust fund sales	51	63
Cost of removal, net of salvage	(19)	(26)
Change in construction payables, net	(50)	5
Other investing activities	(6)	(2)
Net cash used for investing activities	(564)	(329)
Financing Activities:
Increase (decrease) in notes payable, net	245	0
Proceeds —
Senior notes	0	550
Capital contributions from parent company	484	314
Redemptions and repurchases —
Redemptions — Senior notes	0	(200)
Payment of common stock dividends	(202)	(179)
Other financing activities	(9)	(8)
Net cash provided from financing activities	518	477
Net Change in Cash, Cash Equivalents, and Restricted Cash	109	276
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	544	420
Cash, Cash Equivalents, and Restricted Cash at End of Period	653	696
Cash paid (received) during the period for —
Interest	84	84
Income taxes, net	9	0
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	195	90
GEORGIA POWER CO
Operating Activities:
Net income	352	264
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	280	271
Deferred income taxes	(38)	71
Deferred expenses	35	38
Pension, postretirement, and other employee benefits	(19)	(21)
Settlement of asset retirement obligations	(23)	(22)
Other, net	(7)	(42)
Changes in certain current assets and liabilities —
-Receivables	135	142
-Fossil fuel stock	24	(38)
-Prepaid income taxes	84	5
-Other current assets	9	(16)
-Accounts payable	(180)	(155)
-Accrued taxes	(191)	(235)
-Accrued compensation	(85)	(87)
-Retail fuel cost over recovery	0	(66)
-Other current liabilities	(3)	2
Net cash provided from operating activities	373	111
Investing Activities:
Property additions	(681)	(556)
Nuclear decommissioning trust fund purchases	(255)	(161)
Nuclear decommissioning trust fund sales	250	155
Cost of removal, net of salvage	(26)	(17)
Change in construction payables, net of joint owner portion	(47)	(36)
Payments pursuant to LTSAs	(43)	(22)
Asset dispositions	134	63
Other investing activities	0	8
Net cash used for investing activities	(668)	(566)
Financing Activities:
Increase (decrease) in notes payable, net	0	(391)
Proceeds —
Senior notes	0	850
Capital contributions from parent company	1,474	345
Redemptions and repurchases —
Pollution control revenue bonds	(278)	0
Short-term borrowings	(150)	0
Redemptions — Other long-term debt	(100)	0
Payment of common stock dividends	(339)	(320)
Other financing activities	(6)	(11)
Net cash provided from financing activities	601	473
Net Change in Cash, Cash Equivalents, and Restricted Cash	306	18
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	852	3
Cash, Cash Equivalents, and Restricted Cash at End of Period	1,158	21
Cash paid (received) during the period for —
Interest	115	88
Income taxes, net	0	(5)
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	525	320
GULF POWER CO
Operating Activities:
Net income	42	20
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	49	20
Loss on Plant Scherer Unit 3	0	33
Other, net	1	3
Changes in certain current assets and liabilities —
-Receivables	46	(1)
-Fossil fuel stock	(14)	12
-Other current assets	5	6
-Accounts payable	(28)	(8)
-Accrued taxes	12	(4)
-Accrued compensation	(21)	(23)
-Over recovered regulatory clause revenues	(1)	(18)
-Other current liabilities	13	10
Net cash provided from operating activities	104	50
Investing Activities:
Property additions	(70)	(46)
Cost of removal, net of salvage	(11)	(2)
Change in construction payables, net	12	(7)
Other investing activities	(2)	(2)
Net cash used for investing activities	(71)	(57)
Financing Activities:
Increase (decrease) in notes payable, net	16	(168)
Proceeds —
Capital contributions from parent company	2	4
Common stock	0	175
Redemptions and repurchases —
Payment of common stock dividends	(39)	(31)
Other financing activities	(1)	3
Net cash provided from financing activities	(22)	(17)
Net Change in Cash, Cash Equivalents, and Restricted Cash	11	(24)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	28	56
Cash, Cash Equivalents, and Restricted Cash at End of Period	39	32
Cash paid (received) during the period for —
Interest	1	2
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	38	26
MISSISSIPPI POWER CO
Operating Activities:
Net income	(7)	(20)
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	44	49
Deferred income taxes	155	(47)
Allowance for equity funds used during construction	0	(35)
Estimated loss on Kemper IGCC	37	108
Other, net	3	(3)
Changes in certain current assets and liabilities —
-Receivables	(129)	5
-Other current assets	(12)	13
-Accounts payable	(21)	(35)
-Accrued taxes	(110)	(46)
-Accrued compensation	(22)	(22)
-Over recovered regulatory clause revenues	9	(12)
-Other current liabilities	(9)	5
Net cash provided from operating activities	(62)	(40)
Investing Activities:
Property additions	(33)	(186)
Payments pursuant to LTSAs	(9)	1
Other investing activities	(10)	(5)
Net cash used for investing activities	(52)	(190)
Financing Activities:
Increase (decrease) in notes payable, net	(4)	9
Proceeds —
Senior notes	600	0
Short-term borrowings	300	4
Redemptions and repurchases —
Redemptions — Other long-term debt	(900)	0
Other financing activities	(5)	(1)
Net cash provided from financing activities	(9)	12
Net Change in Cash, Cash Equivalents, and Restricted Cash	(123)	(218)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	248	224
Cash, Cash Equivalents, and Restricted Cash at End of Period	125	6
Cash paid (received) during the period for —
Interest	21	13
Income taxes, net	19	0
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	30	78
SOUTHERN POWER CO
Operating Activities:
Net income	115	66
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	122	127
Deferred income taxes	(50)	36
Amortization of investment tax credits	(14)	(14)
Deferred revenues	14	27
Other, net	15	5
Changes in certain current assets and liabilities —
-Receivables	48	(7)
-Prepaid income taxes	(32)	(21)
-Other current assets	5	(6)
-Accounts payable	(43)	(38)
-Accrued taxes	9	(40)
-Other current liabilities	(12)	15
Net cash provided from operating activities	149	96
Investing Activities:
Business acquisitions, net of cash acquired	(46)	(1,004)
Property additions	(121)	(69)
Change in construction payables, net	25	(125)
Payments pursuant to LTSAs	(18)	(31)
Other investing activities	7	(2)
Net cash used for investing activities	(153)	(1,231)
Financing Activities:
Increase (decrease) in notes payable, net	29	171
Redemptions and repurchases —
Distributions to noncontrolling interests	(13)	(18)
Capital contributions from noncontrolling interests	8	71
Payment of common stock dividends	(78)	(79)
Other financing activities	0	(12)
Net cash provided from financing activities	(54)	133
Net Change in Cash, Cash Equivalents, and Restricted Cash	(58)	(1,002)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	140	1,112
Cash, Cash Equivalents, and Restricted Cash at End of Period	82	110
Cash paid (received) during the period for —
Interest	29	28
Income taxes, net	(39)	(1)
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	57	53
SOUTHERN Co GAS
Operating Activities:
Net income	279	239
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	129	120
Deferred income taxes	47	46
Mark-to-market adjustments	(59)	(82)
Goodwill impairment	42	0
Other, net	(2)	26
Changes in certain current assets and liabilities —
-Receivables	175	115
-Natural gas for sale, net of temporary LIFO liquidation	413	411
-Prepaid income taxes	21	24
-Other current assets	14	19
-Accounts payable	(119)	(216)
-Accrued taxes	28	19
-Accrued compensation	(38)	(14)
-Other current liabilities	48	49
Net cash provided from operating activities	978	756
Investing Activities:
Property additions	(268)	(301)
Cost of removal, net of salvage	(14)	(11)
Change in construction payables, net	(46)	(12)
Investment in unconsolidated subsidiaries	(29)	(81)
Other investing activities	(4)	2
Net cash used for investing activities	(361)	(403)
Financing Activities:
Increase (decrease) in notes payable, net	(483)	(234)
Redemptions and repurchases —
Payment of common stock dividends	(118)	(111)
Other financing activities	6	1
Net cash provided from financing activities	(595)	(344)
Net Change in Cash, Cash Equivalents, and Restricted Cash	22	9
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	78	24
Cash, Cash Equivalents, and Restricted Cash at End of Period	100	33
Cash paid (received) during the period for —
Interest	52	41
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	$ 89	$ 53