RETIREMENT BENEFITS - Components of Accumulated OCI and Changes in Regulatory Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 29,039	$ 25,528	$ 26,612
Total other comprehensive income (loss)	(118)	26	(9)
Ending balance	31,759	29,039	25,528
Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(82)
Total other comprehensive income (loss)	(60)
Ending balance	(142)	(82)
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(3)	(3)
Net (gain) loss	188	100
Total AOCI	185	97
Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	13	17
Net (gain) loss	3,980	3,441
Regulatory amortization	0	0
Regulatory asset	3,993	3,458
Pension plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	97	107
Reclassification adjustments		(9)
Total other comprehensive income (loss)		(10)
Ending balance	185	97	107
Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	3,458	3,155
Reclassification adjustments	(122)	(208)
Total other comprehensive income (loss)	535	303
Ending balance	3,993	3,458	3,155
Pension plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(88)	(7)
Reclassification adjustments		(9)
Pension plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(801)	(498)
Reclassification adjustments	(119)	(204)
Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		(1)
Reclassification adjustments	(3)	(4)
Pension plans | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		8
Pension plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		(12)
Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Pension plans | Change in prior year service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	144
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	1	1
Net (gain) loss	1	(5)
Total AOCI	2	(4)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	1
Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	11	14
Net (gain) loss	110	8
Regulatory amortization	0	0
Regulatory asset	121	22
Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(4)	4
Total other comprehensive income (loss)	6	(8)
Ending balance	2	(4)	4
Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	22	341
Reclassification adjustments	(1)	(21)
Total other comprehensive income (loss)	99	(319)
Ending balance	121	22	341
Other postretirement benefit plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	5	(8)
Other postretirement benefit plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(90)	298
Reclassification adjustments	2	(14)
Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(5)	0
Reclassification adjustments	(3)	(7)
Other postretirement benefit plans | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Other postretirement benefit plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(5)
Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Alabama Power
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	7,477	6,829	6,323
Total other comprehensive income (loss)	4	4	4
Ending balance	8,955	7,477	6,829
Alabama Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Alabama Power | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	6	6
Net (gain) loss	1,124	949
Regulatory amortization	0	0
Regulatory asset	1,130	955
Alabama Power | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	955	890
Reclassification adjustments	(38)	(55)
Total other comprehensive income (loss)	175	65
Ending balance	1,130	955	890
Alabama Power | Pension plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(213)	(120)
Reclassification adjustments	(37)	(54)
Alabama Power | Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Reclassification adjustments	(1)	(1)
Alabama Power | Pension plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Alabama Power | Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Alabama Power | Pension plans | Change in prior year service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	0
Alabama Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Alabama Power | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	3	8
Net (gain) loss	(2)	(16)
Regulatory amortization	0	0
Regulatory asset	1
Regulatory liabilities		(8)
Alabama Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(9)	56
Reclassification adjustments	(4)	(5)
Total other comprehensive income (loss)	10	(65)
Ending balance	1	(9)	56
Alabama Power | Other postretirement benefit plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(14)	60
Reclassification adjustments	0	(1)
Alabama Power | Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	0	0
Reclassification adjustments	(4)	(4)
Alabama Power | Other postretirement benefit plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	0
Alabama Power | Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Georgia Power
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	14,323	11,931	11,356
Total other comprehensive income (loss)	(42)	3	3
Ending balance	15,065	14,323	11,931
Georgia Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Georgia Power | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	10	12
Net (gain) loss	1,406	1,218
Regulatory amortization	0	0
Regulatory asset	1,416	1,230
Georgia Power | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	1,230	1,105
Reclassification adjustments	(45)	(71)
Total other comprehensive income (loss)	186	125
Ending balance	1,416	1,230	1,105
Georgia Power | Pension plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(231)	(196)
Reclassification adjustments	(44)	(69)
Georgia Power | Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Reclassification adjustments	(1)	(2)
Georgia Power | Pension plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Georgia Power | Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Georgia Power | Pension plans | Change in prior year service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	0
Georgia Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Georgia Power | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	4	4
Net (gain) loss	92	56
Regulatory amortization	0	0
Regulatory asset	96	60
Georgia Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	60	202
Reclassification adjustments	(1)	(10)
Total other comprehensive income (loss)	36	(142)
Ending balance	96	60	202
Georgia Power | Other postretirement benefit plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(37)	132
Reclassification adjustments	(1)	(9)
Georgia Power | Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	0	0
Reclassification adjustments	0	(1)
Georgia Power | Other postretirement benefit plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	0
Georgia Power | Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Mississippi Power
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	1,609	1,358	2,943
Total other comprehensive income (loss)	1	0	0
Ending balance	1,652	1,609	1,358
Mississippi Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Mississippi Power | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	2	2
Net (gain) loss	201	165
Regulatory amortization	0	0
Regulatory asset	203	167
Mississippi Power | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	167	158
Reclassification adjustments	(6)	(10)
Total other comprehensive income (loss)	36	9
Ending balance	203	167	158
Mississippi Power | Pension plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(42)	(19)
Reclassification adjustments	(6)	(10)
Mississippi Power | Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Reclassification adjustments	0	0
Mississippi Power | Pension plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Mississippi Power | Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Mississippi Power | Pension plans | Change in prior year service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	0
Mississippi Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Mississippi Power | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	0	0
Net (gain) loss	10	4
Regulatory amortization	0	0
Regulatory asset	10	4
Mississippi Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	4	17
Reclassification adjustments	0	(1)
Total other comprehensive income (loss)	6	(13)
Ending balance	10	4	17
Mississippi Power | Other postretirement benefit plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(6)	12
Reclassification adjustments	0	(1)
Mississippi Power | Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	0	0
Reclassification adjustments	0	0
Mississippi Power | Other postretirement benefit plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	0
Mississippi Power | Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Southern Power
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	7,284	6,498	5,675
Total other comprehensive income (loss)	(42)	14	(10)
Ending balance	6,622	7,284	6,498
Southern Power | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(20)
Total other comprehensive income (loss)	(17)
Ending balance	(37)	(20)
Southern Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	0	0
Net (gain) loss	46	26
Total AOCI	46	26
Southern Power | Pension plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	26	33
Reclassification adjustments		(2)
Total other comprehensive income (loss)		(7)
Ending balance	46	26	33
Southern Power | Pension plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(20)	5
Reclassification adjustments		(2)
Southern Power | Pension plans | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Southern Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	0	0
Net (gain) loss	2	1
Total AOCI	2	1
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0
Southern Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	1	3
Total other comprehensive income (loss)	1	(2)
Ending balance	2	1	3
Southern Power | Other postretirement benefit plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	1	(2)
Southern Power | Other postretirement benefit plans | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Southern Company Gas
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	8,570	9,022	9,109
Total other comprehensive income (loss)	(19)	2	(5)
Ending balance	9,506	8,570	9,022
Southern Company Gas | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	29
Total other comprehensive income (loss)	(16)
Ending balance	13	29
Southern Company Gas | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(6)	(6)
Net (gain) loss	(8)	(38)
Total AOCI	(14)	(44)
Regulatory asset	252	268
Southern Company Gas | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(15)	(17)
Net (gain) loss	113	83
Regulatory amortization	74	94
Regulatory asset	172	160
Southern Company Gas | Pension plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(44)	(42)
Reclassification adjustments		0
Total other comprehensive income (loss)		(2)
Ending balance	(14)	(44)	(42)
Southern Company Gas | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	160	217
Reclassification adjustments	(18)	(25)
Total other comprehensive income (loss)	12	(57)
Ending balance	172	160	217
Southern Company Gas | Pension plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(30)	(6)
Reclassification adjustments		0
Southern Company Gas | Pension plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(30)	(20)
Reclassification adjustments	0	(12)
Southern Company Gas | Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		18
Reclassification adjustments	2	2
Southern Company Gas | Pension plans | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		8
Southern Company Gas | Pension plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		34
Southern Company Gas | Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	(20)	(15)
Southern Company Gas | Pension plans | Change in prior year service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	0
Southern Company Gas | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	1	1
Net (gain) loss	(5)	(5)
Total AOCI	(4)	(4)
Regulatory asset	50	57
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0
Southern Company Gas | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	1	2
Net (gain) loss	(43)	(43)
Regulatory amortization	31	37
Regulatory liabilities	(11)	(4)
Southern Company Gas | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(4)	(3)
Total other comprehensive income (loss)	0	(1)
Ending balance	(4)	(4)	(3)
Southern Company Gas | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(4)	46
Reclassification adjustments	(6)	(6)
Total other comprehensive income (loss)	(7)	(50)
Ending balance	(11)	(4)	$ 46
Southern Company Gas | Other postretirement benefit plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	0	(2)
Southern Company Gas | Other postretirement benefit plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	1	42
Reclassification adjustments	0	0
Southern Company Gas | Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	0	2
Reclassification adjustments	0	0
Southern Company Gas | Other postretirement benefit plans | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		1
Southern Company Gas | Other postretirement benefit plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	0
Southern Company Gas | Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	$ (6)	$ (6)