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REGULATORY MATTERS (Tables) | 12 Months Ended
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Dec. 31, 2023
Regulated Operations [Abstract] |
Schedule of regulatory assets | Details of regulatory assets and (liabilities) reflected in the balance sheets at December 31, 2023 and 2022 are provided in the following tables:
| Southern Company | Alabama Power | Georgia Power | Mississippi Power | Southern Company Gas
| (in millions)
At December 31, 2023 |  |  |  |  |
AROs(a)(w) | $ | 5,733 |  | $ | 1,936 |  | $ | 3,505 |  | $ | 247 |  | $ | — |
Retiree benefit plans(b)(w) | 3,011 |  | 815 |  | 976 |  | 140 |  | 146 |
Remaining net book value of retired assets(c) | 1,357 |  | 499 |  | 841 |  | 17 |  | — |
Deferred income tax charges(d) | 897 |  | 262 |  | 605 |  | 28 |  | — |
Under recovered regulatory clause revenues(e) | 413 |  | 381 |  | — |  | 12 |  | 20 |
Fuel-hedging (realized and unrealized) losses(f) | 270 |  | 100 |  | 121 |  | 49 |  | — |
Deferred depreciation(g) | 270 |  | 143 |  | 127 |  | — |  | — |
Environmental remediation(h)(w) | 255 |  | — |  | 20 |  | — |  | 235 |
Loss on reacquired debt(i) | 238 |  | 35 |  | 197 |  | 5 |  | 1 |
Vacation pay(j)(w) | 217 |  | 83 |  | 107 |  | 11 |  | 16 |
Software and cloud computing costs(k) | 150 |  | 59 |  | 84 |  | 2 |  | 5 |
Regulatory clauses(l) | 140 |  | 112 |  | — |  | — |  | 28 |
Storm damage(m) | 92 |  | — |  | 54 |  | 38 |  | — |
Nuclear outage(n) | 83 |  | 50 |  | 33 |  | — |  | — |
Long-term debt fair value adjustment(o) | 60 |  | — |  | — |  | — |  | 60 |
Qualifying repairs of natural gas distribution systems(p) | 40 |  | — |  | — |  | — |  | 40 |
Plant Daniel Units 3 and 4(q) | 25 |  | — |  | — |  | 25 |  | — |
Kemper County energy facility assets, net(r) | 7 |  | — |  | — |  | 7 |  | — |
Other regulatory assets(s) | 182 |  | 39 |  | 33 |  | 18 |  | 93 |
Deferred income tax credits(d) | (4,686) |  | (1,506) |  | (2,161) |  | (241) |  | (759) |
Other cost of removal obligations(a) | (1,312) |  | 28 |  | 617 |  | (186) |  | (1,771) |
Over recovered regulatory clause revenues(e) | (287) |  | (3) |  | (46) |  | — |  | (238) |
Reliability reserves(t) | (179) |  | (143) |  | — |  | (36) |  | — |
Storm/property damage reserves(t) | (120) |  | (76) |  | — |  | (44) |  | — |
Customer refunds(u) | (19) |  | (15) |  | (4) |  | — |  | — |
Fuel-hedging (realized and unrealized) gains(f) | (6) |  | (5) |  | (1) |  |  | — |
Other regulatory liabilities(v) | (308) |  | (74) |  | (18) |  | (2) |  | (101) |
Total regulatory assets (liabilities), net | $ | 6,523 |  | $ | 2,720 |  | $ | 5,090 |  | $ | 90 |  | $ | (2,225) |
| Southern Company | Alabama Power | Georgia Power | Mississippi Power | Southern Company Gas
| (in millions)
At December 31, 2022 |  |  |  |  |
AROs(a)(w) | $ | 6,096 |  | $ | 1,971 |  | $ | 3,829 |  | $ | 242 |  | $ | — |
Retiree benefit plans(b)(w) | 2,517 |  | 675 |  | 848 |  | 113 |  | 114 |
Remaining net book value of retired assets(c) | 1,543 |  | 562 |  | 962 |  | 19 |  | — |
Under recovered regulatory clause revenues(e) | 953 |  | 788 |  | — |  | 31 |  | 134 |
Deferred income tax charges(d) | 866 |  | 250 |  | 583 |  | 30 |  | — |
Environmental remediation(h)(w) | 294 |  | — |  | 25 |  | — |  | 269 |
Loss on reacquired debt(i) | 257 |  | 38 |  | 213 |  | 5 |  | 1 |
Vacation pay(j)(w) | 212 |  | 82 |  | 108 |  | 10 |  | 12 |
Regulatory clauses(l) | 142 |  | 142 |  | — |  | — |  | — |
Software and cloud computing costs(k) | 111 |  | 46 |  | 59 |  | — |  | 6 |
Nuclear outage(n) | 82 |  | 52 |  | 30 |  | — |  | — |
Long-term debt fair value adjustment(o) | 69 |  | — |  | — |  | — |  | 69 |
Fuel-hedging (realized and unrealized) losses(f) | 60 |  | 15 |  | 45 |  | — |  | — |
Storm damage(m) | 44 |  | — |  | — |  | 44 |  | — |
Plant Daniel Units 3 and 4(q) | 27 |  | — |  | — |  | 27 |  | — |
Qualifying repairs of natural gas distribution systems(p) | 26 |  | — |  | — |  | — |  | 26 |
Kemper County energy facility assets, net(r) | 20 |  | — |  | — |  | 20 |  | — |
Other regulatory assets(s) | 171 |  | 36 |  | 27 |  | 16 |  | 92 |
Deferred income tax credits(d) | (5,251) |  | (1,925) |  | (2,244) |  | (269) |  | (788) |
Other cost of removal obligations(a) | (1,430) |  | 11 |  | 462 |  | (196) |  | (1,707) |
Storm/property damage reserves(t) | (216) |  | (97) |  | (83) |  | (36) |  | — |
Reliability reserves(t) | (191) |  | (166) |  | — |  | (25) |  | — |
Customer refunds(u) | (183) |  | (62) |  | (121) |  | — |  | — |
Fuel-hedging (realized and unrealized) gains(f) | (83) |  | (38) |  | (21) |  | (24) |  | — |
Over recovered regulatory clause revenues(e) | (64) |  | — |  | (38) |  | — |  | (26) |
Other regulatory liabilities(v) | (239) |  | (40) |  | (21) |  | (3) |  | (93) |
Total regulatory assets (liabilities), net | $ | 5,833 |  | $ | 2,340 |  | $ | 4,663 |  | $ | 4 |  | $ | (1,891) |
Unless otherwise noted, the following recovery and amortization periods for these regulatory assets and (liabilities) have been approved by the respective state PSC or regulatory agency: (a)AROs and other cost of removal obligations generally are recorded over the related property lives, which may range up to 64 years for Alabama Power, 56 years for Georgia Power, 55 years for Mississippi Power, and 85 years for Southern Company Gas. AROs and cost of removal obligations are settled and trued up following completion of the related activities. Alabama Power is recovering CCR ARO expenditures over a 38-year period ending in 2054 through Rate CNP Compliance. Effective January 1, 2023, Georgia Power is recovering CCR ARO expenditures over four-year periods through its ECCR tariff. Prior to 2023, expenditures were recovered over three-year periods. See "Georgia Power – Rate Plans" herein and Note 6 for additional information. (b)Recovered and amortized over the average remaining service period, which may range up to 13 years for Alabama Power and Mississippi Power and up to 14 years for Georgia Power and Southern Company Gas. Southern Company's balances also include amounts at SCS and Southern Nuclear that are allocated to the applicable regulated utilities. See Note 11 for additional information. (c)Alabama Power: Primarily represents the net book value of Plant Gorgas Unit 10 ($451 million at December 31, 2023) being amortized over 14 years (through 2037) and Plant Barry Unit 4 ($39 million at December 31, 2023) being amortized over 11 years (through 2034). See "Alabama Power – Environmental Accounting Order" herein for additional information. Georgia Power: Net book values of Plant Wansley Units 1 and 2, Plant Hammond Units 1 through 4, and Plant Branch Unit 4 (totaling $488 million, $339 million, and $8 million, respectively, at December 31, 2023) are being amortized over remaining periods between one and 12 years (between 2024 and 2035). Balance also includes unusable materials and supplies inventories, for which the Georgia PSC will determine a recovery period in a future base rate case. Mississippi Power: Represents net book value of certain environmental compliance assets at Plant Watson and Plant Greene County. The retail portion is being amortized over a 10-year period through 2030 and the wholesale portion is being amortized over a 14-year period through 2035. See "Mississippi Power – Environmental Compliance Overview Plan" herein for additional information. (d)Deferred income tax charges are recovered and deferred income tax credits are primarily amortized over the related property lives, which may range up to 64 years for Alabama Power, 56 years for Georgia Power, 55 years for Mississippi Power, and 85 years for Southern Company Gas. See Note 10 for additional information. As a result of the Tax Reform Legislation, these accounts include certain deferred income tax assets and liabilities not subject to normalization, as described further below: Alabama Power: Related amounts at December 31, 2023 include excess federal deferred income tax liabilities that are available for the benefit of customers in 2024 and/or 2025, as discussed under "Alabama Power – Excess Accumulated Deferred Income Tax Accounting Order" herein. Remaining amounts are being recovered and amortized ratably over the related property lives. Georgia Power: Related amounts include $145 million of deferred income tax assets related to construction costs for Plant Vogtle Units 3 and 4 to be recovered over a 10-year period beginning the month after Unit 4 achieves commercial operation. See "Georgia Power – Nuclear Construction – Regulatory Matters" herein for additional information on recovery of costs related to Plant Vogtle Units 3 and 4. Mississippi Power: Related amounts include retail deferred income tax liabilities ($11 million at December 31, 2023) that are expected to be fully amortized through 2024. Southern Company Gas: Related amounts include deferred income tax liabilities ($1 million at December 31, 2023) being amortized through 2024. See "Southern Company Gas – Rate Proceedings" herein for additional information. (e)Alabama Power: Balances are recorded monthly and expected to be recovered over periods of up to seven years, with the majority expected to be recovered within one year. See "Alabama Power – Rate CNP PPA," " – Rate CNP Compliance," and " – Rate ECR" herein for additional information. Georgia Power: Balances are recorded monthly and expected to be recovered or returned within two years. See "Georgia Power – Rate Plans" herein for additional information. Mississippi Power: At December 31, 2023, $12 million is expected to be recovered through various rate recovery mechanisms over a period to be determined in future rate filings. See "Mississippi Power – Ad Valorem Tax Adjustment" herein for additional information. Southern Company Gas: Balances are recorded and recovered or amortized over periods generally not exceeding five years. In addition to natural gas cost recovery mechanisms, the natural gas distribution utilities have various other cost recovery mechanisms for the recovery of costs, including those related to infrastructure replacement programs. (f)Fuel-hedging assets and liabilities are recorded over the life of the underlying hedged purchase contracts. Upon final settlement, actual costs incurred are recovered through the applicable traditional electric operating company's fuel cost recovery mechanism. Purchase contracts generally do not exceed three and a half years for Alabama Power, three years for Georgia Power, and four years for Mississippi Power. (g)Alabama Power: Represents deferred depreciation expense for Plant Barry Unit 5 ($57 million at December 31, 2023) and Plant Barry common coal assets ($24 million at December 31, 2023) to be amortized until 2036 beginning when Plant Barry Unit 5 is retired and Plant Gaston Unit 5 coal assets ($62 million at December 31, 2023) to be amortized until 2039 beginning when the assets are retired. Georgia Power: Represents deferred depreciation expense for Plant Scherer Units 1 through 3 ($70 million at December 31, 2023) to be amortized over six years beginning in 2029 and Plant Bowen Units 1 and 2 ($40 million at December 31, 2023) to be amortized over four years beginning in 2031, both as approved under Georgia Power's 2022 ARP, and Plant Vogtle Unit 3 and common facilities ($17 million at December 31, 2023) to be amortized over a 10-year period beginning the month after Plant Vogtle Unit 4 achieves commercial operation. See "Georgia Power – Nuclear Construction – Regulatory Matters" herein for additional information on recovery of costs related to Plant Vogtle Units 3 and 4. (h)Effective January 1, 2023, Georgia Power is recovering $5 million annually for environmental remediation under the 2022 ARP. Southern Company Gas' costs are recovered through environmental cost recovery mechanisms when the remediation work is performed. See Note 3 under "Environmental Remediation" for additional information. (i)Recovered over either the remaining life of the original issue or, if refinanced, over the remaining life of the new issue. At December 31, 2023, the remaining amortization periods do not exceed 24 years for Alabama Power, 29 years for Georgia Power, 18 years for Mississippi Power, and four years for Southern Company Gas. (j)Recorded as earned by employees and recovered as paid, generally within one year. Includes both vacation and banked holiday pay, if applicable. (k)Represents certain deferred operations and maintenance costs associated with software and cloud computing projects. For Alabama Power, costs are amortized ratably over the life of the related software, which ranges up to 10 years (through 2034). See "Alabama Power – Software Accounting Order" herein for additional information. For Georgia Power, costs incurred through 2022 are being amortized over five years (through 2027) and the recovery period for costs incurred after 2022 will be determined in its next base rate case. For Mississippi Power, the recovery period will be determined in Mississippi Power's annual PEP filing process. For Southern Company Gas, costs are being amortized ratably over the life of the related software, which ranges up to 10 years (through 2034). (l)Alabama Power: Effective January 1, 2023, balance is being amortized through Rate RSE over a five-year period ending in 2027. Southern Company Gas: Represents amounts related to Nicor Gas' volume balancing adjustment rider expected to be recovered over a period of less than two years. (m)See "Georgia Power – Storm Damage Recovery" herein and Note 1 under "Storm Damage and Reliability Reserves" for additional information. Mississippi Power's balance represents deferred storm costs associated with Hurricanes Ida and Zeta being recovered through PEP over a seven-year period through 2029. (n)Nuclear outage costs are deferred to a regulatory asset when incurred and amortized over a subsequent period of 18 months for Alabama Power and up to 24 months for Georgia Power. See Note 5 for additional information. (o)Recovered over the remaining lives of the original debt issuances at acquisition, which range up to 15 years at December 31, 2023. (p)Represents deferred costs of certain repairs at Atlanta Gas Light being amortized over 20 years. (q)Represents the difference between Mississippi Power's revenue requirement for Plant Daniel Units 3 and 4 under purchase accounting and operating lease accounting. At December 31, 2023, consists of the $17 million retail portion being amortized through 2039 over the remaining life of the related property and the $8 million wholesale portion being amortized through 2035. (r)At December 31, 2023, includes $9 million of regulatory assets (wholesale) expected to be fully amortized by 2035 and $2 million of regulatory liabilities (retail) expected to be fully amortized by 2024. (s)Comprised of numerous immaterial components with remaining amortization periods at December 31, 2023 generally not exceeding 20 years for Alabama Power, 10 years for Georgia Power, 14 years for Mississippi Power, and 15 years for Southern Company Gas. (t)Utilized as related expenses are incurred. See "Alabama Power – Rate NDR" and " – Reliability Reserve Accounting Order," "Georgia Power – Storm Damage Recovery," and "Mississippi Power – System Restoration Rider" and " – Reliability Reserve Accounting Order" herein and Note 1 under "Storm Damage and Reliability Reserves" for additional information. (u)Primarily includes approximately $15 million and $62 million at December 31, 2023 and 2022, respectively, for Alabama Power and $119 million at December 31, 2022 for Georgia Power as a result of each company exceeding its allowed retail return range. Georgia Power's balances also include immaterial amounts related to refunds for transmission service customers. See "Alabama Power – Rate RSE" and "Georgia Power – Rate Plans" herein for additional information. (v)Comprised of numerous immaterial components with remaining amortization periods at December 31, 2023 generally not exceeding 11 years for Alabama Power, nine years for Georgia Power, four years for Mississippi Power, and 20 years for Southern Company Gas. (w)Generally not earning a return as they are excluded from rate base or are offset in rate base by a corresponding asset or liability. The following table illustrates Southern Company Gas' authorized ratemaking amounts that are not recognized on its balance sheets. These amounts are primarily comprised of an allowed equity rate of return on assets associated with certain regulatory infrastructure programs. These amounts will be recognized as revenues in Southern Company Gas' financial statements in the periods they are billable to customers, the majority of which will be recovered by 2025.
| December 31, 2023 |  | December 31, 2022
| (in millions)
Atlanta Gas Light | $ | 23 |  |  | $ | 35 |
Virginia Natural Gas | 10 |  |  | 10 |
Chattanooga Gas | 7 |  |  | 2 |
Nicor Gas | 3 |  |  | 3 |
Total | $ | 43 |  |  | $ | 50 |
Schedule of regulatory liabilities | Details of regulatory assets and (liabilities) reflected in the balance sheets at December 31, 2023 and 2022 are provided in the following tables:
| Southern Company | Alabama Power | Georgia Power | Mississippi Power | Southern Company Gas
| (in millions)
At December 31, 2023 |  |  |  |  |
AROs(a)(w) | $ | 5,733 |  | $ | 1,936 |  | $ | 3,505 |  | $ | 247 |  | $ | — |
Retiree benefit plans(b)(w) | 3,011 |  | 815 |  | 976 |  | 140 |  | 146 |
Remaining net book value of retired assets(c) | 1,357 |  | 499 |  | 841 |  | 17 |  | — |
Deferred income tax charges(d) | 897 |  | 262 |  | 605 |  | 28 |  | — |
Under recovered regulatory clause revenues(e) | 413 |  | 381 |  | — |  | 12 |  | 20 |
Fuel-hedging (realized and unrealized) losses(f) | 270 |  | 100 |  | 121 |  | 49 |  | — |
Deferred depreciation(g) | 270 |  | 143 |  | 127 |  | — |  | — |
Environmental remediation(h)(w) | 255 |  | — |  | 20 |  | — |  | 235 |
Loss on reacquired debt(i) | 238 |  | 35 |  | 197 |  | 5 |  | 1 |
Vacation pay(j)(w) | 217 |  | 83 |  | 107 |  | 11 |  | 16 |
Software and cloud computing costs(k) | 150 |  | 59 |  | 84 |  | 2 |  | 5 |
Regulatory clauses(l) | 140 |  | 112 |  | — |  | — |  | 28 |
Storm damage(m) | 92 |  | — |  | 54 |  | 38 |  | — |
Nuclear outage(n) | 83 |  | 50 |  | 33 |  | — |  | — |
Long-term debt fair value adjustment(o) | 60 |  | — |  | — |  | — |  | 60 |
Qualifying repairs of natural gas distribution systems(p) | 40 |  | — |  | — |  | — |  | 40 |
Plant Daniel Units 3 and 4(q) | 25 |  | — |  | — |  | 25 |  | — |
Kemper County energy facility assets, net(r) | 7 |  | — |  | — |  | 7 |  | — |
Other regulatory assets(s) | 182 |  | 39 |  | 33 |  | 18 |  | 93 |
Deferred income tax credits(d) | (4,686) |  | (1,506) |  | (2,161) |  | (241) |  | (759) |
Other cost of removal obligations(a) | (1,312) |  | 28 |  | 617 |  | (186) |  | (1,771) |
Over recovered regulatory clause revenues(e) | (287) |  | (3) |  | (46) |  | — |  | (238) |
Reliability reserves(t) | (179) |  | (143) |  | — |  | (36) |  | — |
Storm/property damage reserves(t) | (120) |  | (76) |  | — |  | (44) |  | — |
Customer refunds(u) | (19) |  | (15) |  | (4) |  | — |  | — |
Fuel-hedging (realized and unrealized) gains(f) | (6) |  | (5) |  | (1) |  |  | — |
Other regulatory liabilities(v) | (308) |  | (74) |  | (18) |  | (2) |  | (101) |
Total regulatory assets (liabilities), net | $ | 6,523 |  | $ | 2,720 |  | $ | 5,090 |  | $ | 90 |  | $ | (2,225) |
| Southern Company | Alabama Power | Georgia Power | Mississippi Power | Southern Company Gas
| (in millions)
At December 31, 2022 |  |  |  |  |
AROs(a)(w) | $ | 6,096 |  | $ | 1,971 |  | $ | 3,829 |  | $ | 242 |  | $ | — |
Retiree benefit plans(b)(w) | 2,517 |  | 675 |  | 848 |  | 113 |  | 114 |
Remaining net book value of retired assets(c) | 1,543 |  | 562 |  | 962 |  | 19 |  | — |
Under recovered regulatory clause revenues(e) | 953 |  | 788 |  | — |  | 31 |  | 134 |
Deferred income tax charges(d) | 866 |  | 250 |  | 583 |  | 30 |  | — |
Environmental remediation(h)(w) | 294 |  | — |  | 25 |  | — |  | 269 |
Loss on reacquired debt(i) | 257 |  | 38 |  | 213 |  | 5 |  | 1 |
Vacation pay(j)(w) | 212 |  | 82 |  | 108 |  | 10 |  | 12 |
Regulatory clauses(l) | 142 |  | 142 |  | — |  | — |  | — |
Software and cloud computing costs(k) | 111 |  | 46 |  | 59 |  | — |  | 6 |
Nuclear outage(n) | 82 |  | 52 |  | 30 |  | — |  | — |
Long-term debt fair value adjustment(o) | 69 |  | — |  | — |  | — |  | 69 |
Fuel-hedging (realized and unrealized) losses(f) | 60 |  | 15 |  | 45 |  | — |  | — |
Storm damage(m) | 44 |  | — |  | — |  | 44 |  | — |
Plant Daniel Units 3 and 4(q) | 27 |  | — |  | — |  | 27 |  | — |
Qualifying repairs of natural gas distribution systems(p) | 26 |  | — |  | — |  | — |  | 26 |
Kemper County energy facility assets, net(r) | 20 |  | — |  | — |  | 20 |  | — |
Other regulatory assets(s) | 171 |  | 36 |  | 27 |  | 16 |  | 92 |
Deferred income tax credits(d) | (5,251) |  | (1,925) |  | (2,244) |  | (269) |  | (788) |
Other cost of removal obligations(a) | (1,430) |  | 11 |  | 462 |  | (196) |  | (1,707) |
Storm/property damage reserves(t) | (216) |  | (97) |  | (83) |  | (36) |  | — |
Reliability reserves(t) | (191) |  | (166) |  | — |  | (25) |  | — |
Customer refunds(u) | (183) |  | (62) |  | (121) |  | — |  | — |
Fuel-hedging (realized and unrealized) gains(f) | (83) |  | (38) |  | (21) |  | (24) |  | — |
Over recovered regulatory clause revenues(e) | (64) |  | — |  | (38) |  | — |  | (26) |
Other regulatory liabilities(v) | (239) |  | (40) |  | (21) |  | (3) |  | (93) |
Total regulatory assets (liabilities), net | $ | 5,833 |  | $ | 2,340 |  | $ | 4,663 |  | $ | 4 |  | $ | (1,891) |
Unless otherwise noted, the following recovery and amortization periods for these regulatory assets and (liabilities) have been approved by the respective state PSC or regulatory agency: (a)AROs and other cost of removal obligations generally are recorded over the related property lives, which may range up to 64 years for Alabama Power, 56 years for Georgia Power, 55 years for Mississippi Power, and 85 years for Southern Company Gas. AROs and cost of removal obligations are settled and trued up following completion of the related activities. Alabama Power is recovering CCR ARO expenditures over a 38-year period ending in 2054 through Rate CNP Compliance. Effective January 1, 2023, Georgia Power is recovering CCR ARO expenditures over four-year periods through its ECCR tariff. Prior to 2023, expenditures were recovered over three-year periods. See "Georgia Power – Rate Plans" herein and Note 6 for additional information. (b)Recovered and amortized over the average remaining service period, which may range up to 13 years for Alabama Power and Mississippi Power and up to 14 years for Georgia Power and Southern Company Gas. Southern Company's balances also include amounts at SCS and Southern Nuclear that are allocated to the applicable regulated utilities. See Note 11 for additional information. (c)Alabama Power: Primarily represents the net book value of Plant Gorgas Unit 10 ($451 million at December 31, 2023) being amortized over 14 years (through 2037) and Plant Barry Unit 4 ($39 million at December 31, 2023) being amortized over 11 years (through 2034). See "Alabama Power – Environmental Accounting Order" herein for additional information. Georgia Power: Net book values of Plant Wansley Units 1 and 2, Plant Hammond Units 1 through 4, and Plant Branch Unit 4 (totaling $488 million, $339 million, and $8 million, respectively, at December 31, 2023) are being amortized over remaining periods between one and 12 years (between 2024 and 2035). Balance also includes unusable materials and supplies inventories, for which the Georgia PSC will determine a recovery period in a future base rate case. Mississippi Power: Represents net book value of certain environmental compliance assets at Plant Watson and Plant Greene County. The retail portion is being amortized over a 10-year period through 2030 and the wholesale portion is being amortized over a 14-year period through 2035. See "Mississippi Power – Environmental Compliance Overview Plan" herein for additional information. (d)Deferred income tax charges are recovered and deferred income tax credits are primarily amortized over the related property lives, which may range up to 64 years for Alabama Power, 56 years for Georgia Power, 55 years for Mississippi Power, and 85 years for Southern Company Gas. See Note 10 for additional information. As a result of the Tax Reform Legislation, these accounts include certain deferred income tax assets and liabilities not subject to normalization, as described further below: Alabama Power: Related amounts at December 31, 2023 include excess federal deferred income tax liabilities that are available for the benefit of customers in 2024 and/or 2025, as discussed under "Alabama Power – Excess Accumulated Deferred Income Tax Accounting Order" herein. Remaining amounts are being recovered and amortized ratably over the related property lives. Georgia Power: Related amounts include $145 million of deferred income tax assets related to construction costs for Plant Vogtle Units 3 and 4 to be recovered over a 10-year period beginning the month after Unit 4 achieves commercial operation. See "Georgia Power – Nuclear Construction – Regulatory Matters" herein for additional information on recovery of costs related to Plant Vogtle Units 3 and 4. Mississippi Power: Related amounts include retail deferred income tax liabilities ($11 million at December 31, 2023) that are expected to be fully amortized through 2024. Southern Company Gas: Related amounts include deferred income tax liabilities ($1 million at December 31, 2023) being amortized through 2024. See "Southern Company Gas – Rate Proceedings" herein for additional information. (e)Alabama Power: Balances are recorded monthly and expected to be recovered over periods of up to seven years, with the majority expected to be recovered within one year. See "Alabama Power – Rate CNP PPA," " – Rate CNP Compliance," and " – Rate ECR" herein for additional information. Georgia Power: Balances are recorded monthly and expected to be recovered or returned within two years. See "Georgia Power – Rate Plans" herein for additional information. Mississippi Power: At December 31, 2023, $12 million is expected to be recovered through various rate recovery mechanisms over a period to be determined in future rate filings. See "Mississippi Power – Ad Valorem Tax Adjustment" herein for additional information. Southern Company Gas: Balances are recorded and recovered or amortized over periods generally not exceeding five years. In addition to natural gas cost recovery mechanisms, the natural gas distribution utilities have various other cost recovery mechanisms for the recovery of costs, including those related to infrastructure replacement programs. (f)Fuel-hedging assets and liabilities are recorded over the life of the underlying hedged purchase contracts. Upon final settlement, actual costs incurred are recovered through the applicable traditional electric operating company's fuel cost recovery mechanism. Purchase contracts generally do not exceed three and a half years for Alabama Power, three years for Georgia Power, and four years for Mississippi Power. (g)Alabama Power: Represents deferred depreciation expense for Plant Barry Unit 5 ($57 million at December 31, 2023) and Plant Barry common coal assets ($24 million at December 31, 2023) to be amortized until 2036 beginning when Plant Barry Unit 5 is retired and Plant Gaston Unit 5 coal assets ($62 million at December 31, 2023) to be amortized until 2039 beginning when the assets are retired. Georgia Power: Represents deferred depreciation expense for Plant Scherer Units 1 through 3 ($70 million at December 31, 2023) to be amortized over six years beginning in 2029 and Plant Bowen Units 1 and 2 ($40 million at December 31, 2023) to be amortized over four years beginning in 2031, both as approved under Georgia Power's 2022 ARP, and Plant Vogtle Unit 3 and common facilities ($17 million at December 31, 2023) to be amortized over a 10-year period beginning the month after Plant Vogtle Unit 4 achieves commercial operation. See "Georgia Power – Nuclear Construction – Regulatory Matters" herein for additional information on recovery of costs related to Plant Vogtle Units 3 and 4. (h)Effective January 1, 2023, Georgia Power is recovering $5 million annually for environmental remediation under the 2022 ARP. Southern Company Gas' costs are recovered through environmental cost recovery mechanisms when the remediation work is performed. See Note 3 under "Environmental Remediation" for additional information. (i)Recovered over either the remaining life of the original issue or, if refinanced, over the remaining life of the new issue. At December 31, 2023, the remaining amortization periods do not exceed 24 years for Alabama Power, 29 years for Georgia Power, 18 years for Mississippi Power, and four years for Southern Company Gas. (j)Recorded as earned by employees and recovered as paid, generally within one year. Includes both vacation and banked holiday pay, if applicable. (k)Represents certain deferred operations and maintenance costs associated with software and cloud computing projects. For Alabama Power, costs are amortized ratably over the life of the related software, which ranges up to 10 years (through 2034). See "Alabama Power – Software Accounting Order" herein for additional information. For Georgia Power, costs incurred through 2022 are being amortized over five years (through 2027) and the recovery period for costs incurred after 2022 will be determined in its next base rate case. For Mississippi Power, the recovery period will be determined in Mississippi Power's annual PEP filing process. For Southern Company Gas, costs are being amortized ratably over the life of the related software, which ranges up to 10 years (through 2034). (l)Alabama Power: Effective January 1, 2023, balance is being amortized through Rate RSE over a five-year period ending in 2027. Southern Company Gas: Represents amounts related to Nicor Gas' volume balancing adjustment rider expected to be recovered over a period of less than two years. (m)See "Georgia Power – Storm Damage Recovery" herein and Note 1 under "Storm Damage and Reliability Reserves" for additional information. Mississippi Power's balance represents deferred storm costs associated with Hurricanes Ida and Zeta being recovered through PEP over a seven-year period through 2029. (n)Nuclear outage costs are deferred to a regulatory asset when incurred and amortized over a subsequent period of 18 months for Alabama Power and up to 24 months for Georgia Power. See Note 5 for additional information. (o)Recovered over the remaining lives of the original debt issuances at acquisition, which range up to 15 years at December 31, 2023. (p)Represents deferred costs of certain repairs at Atlanta Gas Light being amortized over 20 years. (q)Represents the difference between Mississippi Power's revenue requirement for Plant Daniel Units 3 and 4 under purchase accounting and operating lease accounting. At December 31, 2023, consists of the $17 million retail portion being amortized through 2039 over the remaining life of the related property and the $8 million wholesale portion being amortized through 2035. (r)At December 31, 2023, includes $9 million of regulatory assets (wholesale) expected to be fully amortized by 2035 and $2 million of regulatory liabilities (retail) expected to be fully amortized by 2024. (s)Comprised of numerous immaterial components with remaining amortization periods at December 31, 2023 generally not exceeding 20 years for Alabama Power, 10 years for Georgia Power, 14 years for Mississippi Power, and 15 years for Southern Company Gas. (t)Utilized as related expenses are incurred. See "Alabama Power – Rate NDR" and " – Reliability Reserve Accounting Order," "Georgia Power – Storm Damage Recovery," and "Mississippi Power – System Restoration Rider" and " – Reliability Reserve Accounting Order" herein and Note 1 under "Storm Damage and Reliability Reserves" for additional information. (u)Primarily includes approximately $15 million and $62 million at December 31, 2023 and 2022, respectively, for Alabama Power and $119 million at December 31, 2022 for Georgia Power as a result of each company exceeding its allowed retail return range. Georgia Power's balances also include immaterial amounts related to refunds for transmission service customers. See "Alabama Power – Rate RSE" and "Georgia Power – Rate Plans" herein for additional information. (v)Comprised of numerous immaterial components with remaining amortization periods at December 31, 2023 generally not exceeding 11 years for Alabama Power, nine years for Georgia Power, four years for Mississippi Power, and 20 years for Southern Company Gas. (w)Generally not earning a return as they are excluded from rate base or are offset in rate base by a corresponding asset or liability.
Public utilities general disclosures | Details of tariff adjustments are provided in the following table:
Tariff | 2023 |  | 2024 |  |
| (in millions)
Traditional base | $ | 194 |  |  | $ | 275 |  |  |
ECCR | (21) |  |  | (99) |  |  |
DSM | 37 |  |  | 10 |  |  |
MFF | 6 |  |  | 5 |  |  |
Total | $ | 216 |  |  | $ | 191 |  |  |
The Georgia PSC approved the following tariff adjustments under the 2019 ARP effective January 1 2022:
Tariff |  |  | 2022
|  |  | (in millions)
Traditional base |  |  | $ | 192 |
ECCR |  |  | (12) |
DSM |  |  | (25) |
MFF |  |  | 2 |
Total |  |  | $ | 157 |
The following table provides regulatory information for Southern Company Gas' natural gas distribution utilities:
| Nicor Gas |  | Atlanta Gas Light |  | Virginia Natural Gas |  | Chattanooga Gas
Authorized ROE at December 31, 2023 | 9.51% |  | 10.25% |  | 9.70% |  | 9.80%
Weather normalization mechanisms(a) |  |  |  |  | ü |  | ü
Decoupled, including straight-fixed-variable rates(b) | ü |  | ü |  | ü |  |
Regulatory infrastructure program rate(c) | ü |  | ü |  | ü |  | ü
Bad debt rider(d) | ü |  |  |  | ü |  | ü
Energy efficiency plan(e) | ü |  |  |  | ü |  |
Annual base rate adjustment mechanism(f) |  |  | ü |  |  |  | ü
Year of last base rate case decision | 2023 |  | 2019 |  | 2023 |  | 2018
(a)Designed to help stabilize operating results by allowing recovery of costs in the event of unseasonal weather, but are not direct offsets to the potential impacts on earnings of weather and customer consumption. (b)Allows for recovery of fixed customer service costs separately from assumed natural gas volumes used by customers and provides a benchmark level of revenue for recovery. (c)See "Infrastructure Replacement Programs and Capital Projects" herein for additional information. Chattanooga Gas' pipeline replacement program costs are recovered through its annual base rate review mechanism. (d)The recovery (refund) of bad debt expense over (under) an established benchmark expense. The gas portion of bad debt expense is recovered through purchased gas adjustment mechanisms. Nicor Gas also has a rider to recover the non-gas portion of bad debt expense. (e)Recovery of costs associated with plans to achieve specified energy savings goals. (f)Regulatory mechanism allowing annual adjustments to base rates up or down based on authorized ROE and/or ROE range. The following table and discussions provide updates on the infrastructure replacement programs and capital projects at the natural gas distribution utilities at December 31, 2023. These programs are risk-based and designed to update and replace cast iron, bare steel, and mid-vintage plastic materials or expand Southern Company Gas' distribution systems to improve reliability and meet operational flexibility and growth.
Utility |  | Program |  |  |  | Recovery |  | Capital Expenditures in 2023 |  | Capital Expenditures Since Project Inception |  | Pipe Installed Since Project Inception |  | Scope of Program |  | Program Duration |  | Last Year of Program
|  |  |  |  |  |  |  | (in millions) |  | (miles) |  | (miles) |  | (years) |  |
Nicor Gas |  | Investing in Illinois Qualifying Infrastructure Plant(*) |  |  |  | Rider |  | $ | 365 |  |  | $ | 3,228 |  |  | 1,367 |  |  | 1,367 |  |  | 9 |  | 2023
Virginia Natural Gas |  | SAVE |  |  |  | Rider |  | 75 |  |  | 486 |  |  | 567 |  |  | 695 |  |  | 13 |  | 2024
Atlanta Gas Light |  | System Reinforcement Rider |  |  |  | Rider |  | 104 |  |  | 180 |  |  | 20 |  |  | N/A |  | 3 |  | 2024
Chattanooga Gas |  | Pipeline Replacement Program |  |  |  | Rate Base |  | 9 |  |  | 16 |  |  | 15 |  |  | 73 |  |  | 7 |  | 2027
Total |  |  |  |  |  |  |  | $ | 553 |  |  | $ | 3,910 |  |  | 1,969 |  |  | 2,135 |  |  |  |  |
(*)Included replacement of pipes, compressors, and transmission mains along with other improvements such as new meters. This program ended November 30, 2023 with all expenditures placed in service. Recovery of program costs is described under "Nicor Gas" herein. The following table provides a summary of QIP capital investments during the nine-year program:
Year | Status of QIP Annual Review Proceeding | Capital Investments |  | Disallowed |  | Month of Disallowance
|  | (in millions) |  |
2015 – 2018 | Complete | $ | 1,246 |  |  | $ | — |  |  |
2019 | Complete(a) | 415 |  |  | 32 |  |  | June 2023
2020 | Filed March 2021 | 402 |  | (b) |  |  |
2021 | Filed March 2022 | 392 |  | (b) |  |  |
2022 | Filed March 2023 | 408 |  | (b) | 6 |  | (a)(c) | November 2023
2023 | To be filed by March 20, 2024 | 365 |  | (b) | 25 |  | (a)(c) | November 2023
| $ | 3,228 |  |  | $ | 63 |  |  |
(a)Appealed to the Illinois Appellate Court. (b)Capital investments are subject to the required QIP annual review proceeding; years 2020 through 2022 are pending with the Illinois Commission. (c)Disallowed in Nicor Gas' 2023 general base rate case proceeding. See "Rate Proceedings – Nicor Gas" herein for additional information regarding the Illinois Commission's disallowance of certain capital investments.
Schedule of revised cost and schedule | Georgia Power's approximate proportionate share of the remaining estimated capital cost to complete Plant Vogtle Units 3 and 4, including contingency, through the second quarter 2024 is as follows:
| (in millions) |
Base project capital cost forecast(a)(b) | $ | 10,717 |  |
Construction contingency estimate | 36 |  |
Total project capital cost forecast(a)(b) | 10,753 |  |
Net investment at December 31, 2023(b) | (10,564) |  |
Remaining estimate to complete | $ | 189 |  |
(a)Includes approximately $610 million of costs that are not shared with the other Vogtle Owners, including $33 million of construction monitoring costs, and approximately $567 million of incremental costs under the cost-sharing provisions of the joint ownership agreements described below. Excludes financing costs expected to be capitalized through AFUDC of approximately $440 million, of which $417 million had been accrued through December 31, 2023. (b)Net of $1.7 billion received from Toshiba under the Guarantee Settlement Agreement and approximately $188 million in related customer refunds.

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