LEASES - Balance Sheet Amounts Recorded for Operating and Financing Leases (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Operating Leases
Operating lease ROU assets, net	$ 1,701	$ 1,802
Operating lease obligations - current	250	241
Operating lease obligations - non-current	1,503	1,611
Total operating lease obligations	$ 1,754	$ 1,852
Finance Leases
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Plant In Service Net Of Depreciation	Plant In Service Net Of Depreciation
Finance lease ROU assets, net	$ 197	$ 218
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Current	Other Liabilities, Current
Finance lease obligations - current	$ 16	$ 17
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-Term Debt	Long-Term Debt
Finance lease obligations - non-current	$ 199	$ 214
Total finance lease obligations	215	231
Assets Subject to Power Purchase Agreement
Operating Leases
Total operating lease obligations	802	941
Alabama Power
Operating Leases
Operating lease ROU assets, net	$ 108	$ 151
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Current	Other Liabilities, Current
Operating lease obligations - current	$ 54	$ 51
Operating lease obligations - non-current	66	119
Total operating lease obligations	$ 121	$ 170
Finance Leases
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Plant In Service Net Of Depreciation	Plant In Service Net Of Depreciation
Finance lease ROU assets, net	$ 4	$ 5
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Current	Other Liabilities, Current
Finance lease obligations - current	$ 1	$ 1
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-Term Debt	Long-Term Debt
Finance lease obligations - non-current	$ 3	$ 4
Total finance lease obligations	4	5
Alabama Power | Assets Subject to Power Purchase Agreement
Operating Leases
Total operating lease obligations	104	146
Georgia Power
Operating Leases
Operating lease ROU assets, net	1,157	1,308
Operating lease obligations - current	156	151
Operating lease obligations - non-current	999	1,156
Total operating lease obligations	$ 1,155	$ 1,307
Finance Leases
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Plant In Service Net Of Depreciation	Plant In Service Net Of Depreciation
Finance lease ROU assets, net	$ 104	$ 115
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Current	Other Liabilities, Current
Finance lease obligations - current	$ 10	$ 9
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-Term Debt	Long-Term Debt
Finance lease obligations - non-current	$ 126	$ 136
Total finance lease obligations	136	145
Georgia Power | Assets Subject to Power Purchase Agreement
Operating Leases
Total operating lease obligations	$ 1,110	$ 1,250
Mississippi Power
Operating Leases
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other Assets, Noncurrent	Other Assets, Noncurrent
Operating lease ROU assets, net	$ 10	$ 9
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Current	Other Liabilities, Current
Operating lease obligations - current	$ 4	$ 2
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Intangible liabilities included in other deferred credits and liabilities	Intangible liabilities included in other deferred credits and liabilities
Operating lease obligations - non-current	$ 6	$ 7
Total operating lease obligations	$ 10	$ 9
Finance Leases
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Plant In Service Net Of Depreciation	Plant In Service Net Of Depreciation
Finance lease ROU assets, net	$ 17	$ 19
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Current	Other Liabilities, Current
Finance lease obligations - current	$ 1	$ 1
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-Term Debt	Long-Term Debt
Finance lease obligations - non-current	$ 17	$ 18
Total finance lease obligations	18	19
Southern Power
Operating Leases
Operating lease ROU assets, net	$ 479	$ 415
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Current	Other Liabilities, Current
Operating lease obligations - current	$ 28	$ 25
Operating lease obligations - non-current	497	426
Total operating lease obligations	525	451
Finance Leases
Finance lease ROU assets, net	0	0
Finance lease obligations - current	0	0
Finance lease obligations - non-current	0	0
Total finance lease obligations	0	0
Southern Company Gas
Operating Leases
Operating lease ROU assets, net	$ 70	$ 81
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Current	Other Liabilities, Current
Operating lease obligations - current	$ 11	$ 15
Operating lease obligations - non-current	59	67
Total operating lease obligations	70	82
Finance Leases
Finance lease ROU assets, net	0	0
Finance lease obligations - current	0	0
Finance lease obligations - non-current	0	0
Total finance lease obligations	$ 0	$ 0