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REGULATORY MATTERS (Tables) | 12 Months Ended
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Dec. 31, 2021
Regulated Operations [Abstract] |
Schedule of regulatory assets | Details of regulatory assets and (liabilities) reflected in the balance sheets at December 31, 2021 and 2020 are provided in the following tables:
| Southern Company | Alabama Power | Georgia Power | Mississippi Power | Southern Company Gas
| (in millions)
At December 31, 2021 |  |  |  |  |
AROs(a)(u) | $ | 5,685 |  | $ | 1,576 |  | $ | 3,866 |  | $ | 236 |  | $ | — |
Retiree benefit plans(b)(u) | 2,998 |  | 747 |  | 962 |  | 145 |  | 95 |
Remaining net book value of retired assets(c) | 1,050 |  | 574 |  | 455 |  | 21 |  | — |
Deferred income tax charges(d) | 829 |  | 240 |  | 555 |  | 31 |  | — |
Under recovered regulatory clause revenues(e) | 806 |  | 225 |  | — |  | 49 |  | 532 |
Environmental remediation(f)(u) | 302 |  | — |  | 35 |  | — |  | 267 |
Loss on reacquired debt(g) | 281 |  | 42 |  | 231 |  | 6 |  | 2 |
Vacation pay(h)(u) | 207 |  | 81 |  | 102 |  | 10 |  | 14 |
Regulatory clauses(i) | 142 |  | 142 |  | — |  | — |  | — |
Storm damage(j) | 97 |  | — |  | 48 |  | 49 |  | — |
Long-term debt fair value adjustment(k) | 79 |  | — |  | — |  | — |  | 79 |
Nuclear outage(l) | 75 |  | 41 |  | 34 |  | — |  | — |
Software and cloud computing costs(m) | 73 |  | 35 |  | 33 |  | — |  | 5 |
Kemper County energy facility assets, net(n) | 35 |  | — |  | — |  | 35 |  | — |
Plant Daniel Units 3 and 4(o) | 28 |  | — |  | — |  | 28 |  | — |
Other regulatory assets(p) | 168 |  | 38 |  | 29 |  | 7 |  | 94 |
Deferred income tax credits(d) | (5,636) |  | (1,968) |  | (2,537) |  | (288) |  | (816) |
Other cost of removal obligations(a) | (1,826) |  | (192) |  | 278 |  | (195) |  | (1,683) |
Customer refunds(q) | (189) |  | (181) |  | (8) |  | — |  | — |
Fuel-hedging (realized and unrealized) gains(r) | (176) |  | (50) |  | (72) |  | (54) |  | — |
Storm/property damage reserves(s) | (133) |  | (103) |  | — |  | (30) |  | — |
Over recovered regulatory clause revenues(e) | (63) |  | (1) |  | (59) |  | — |  | (3) |
Other regulatory liabilities(t) | (121) |  | (29) |  | (24) |  | (4) |  | (57) |
Total regulatory assets (liabilities), net | $ | 4,711 |  | $ | 1,217 |  | $ | 3,928 |  | $ | 46 |  | $ | (1,471) |
| Southern Company | Alabama Power | Georgia Power | Mississippi Power | Southern Company Gas
| (in millions)
At December 31, 2020 |  |  |  |  |
AROs(a)(u) | $ | 5,147 |  | $ | 1,470 |  | $ | 3,457 |  | $ | 212 |  | $ | — |
Retiree benefit plans(b)(u) | 4,958 |  | 1,265 |  | 1,647 |  | 238 |  | 187 |
Remaining net book value of retired assets(c) | 1,183 |  | 632 |  | 527 |  | 24 |  | — |
Deferred income tax charges(d) | 801 |  | 235 |  | 531 |  | 32 |  | — |
Environmental remediation(f)(u) | 310 |  | — |  | 41 |  | — |  | 269 |
Loss on reacquired debt(g) | 304 |  | 47 |  | 248 |  | 6 |  | 3 |
Storm damage(j) | 262 |  | — |  | 262 |  | — |  | — |
Vacation pay(h)(u) | 207 |  | 80 |  | 104 |  | 10 |  | 13 |
Under recovered regulatory clause revenues(e) | 185 |  | 58 |  | — |  | 52 |  | 75 |
Regulatory clauses(i) | 142 |  | 142 |  | — |  | — |  | — |
Nuclear outage(l) | 101 |  | 61 |  | 40 |  | — |  | — |
Long-term debt fair value adjustment(k) | 92 |  | — |  | — |  | — |  | 92 |
Kemper County energy facility assets, net(n) | 50 |  | — |  | — |  | 50 |  | — |
Plant Daniel Units 3 and 4(o) | 32 |  | — |  | — |  | 32 |  | — |
Software and cloud computing costs(m) | 31 |  | 17 |  | 12 |  | — |  | 2 |
Other regulatory assets(p) | 174 |  | 35 |  | 56 |  | 4 |  | 79 |
Deferred income tax credits(d) | (6,016) |  | (2,016) |  | (2,805) |  | (320) |  | (847) |
Other cost of removal obligations(a) | (1,999) |  | (335) |  | 212 |  | (194) |  | (1,649) |
Over recovered regulatory clause revenues(e) | (185) |  | (46) |  | (44) |  | — |  | (95) |
Storm/property damage reserves(s) | (81) |  | (77) |  | — |  | (4) |  | — |
Customer refunds(q) | (56) |  | (50) |  | (6) |  | — |  | — |
Other regulatory liabilities(t) | (149) |  | (37) |  | (30) |  | (6) |  | (54) |
Total regulatory assets (liabilities), net | $ | 5,493 |  | $ | 1,481 |  | $ | 4,252 |  | $ | 136 |  | $ | (1,925) |
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 53 years for Alabama Power, 60 years for Georgia Power, 55 years for Mississippi Power, and 80 years for Southern Company Gas. AROs and cost of removal obligations will be settled and trued up following completion of the related activities. Effective January 1, 2020, Georgia Power is recovering CCR AROs, including past under recovered costs and estimated annual compliance costs, over three-year periods ending December 31, 2022, 2023, and 2024 through its ECCR tariff, as discussed further under "Georgia Power – Rate Plans" herein. See Note 6 for additional information on AROs. (b)Recovered and amortized over the average remaining service period, which may range up to 13 years for Alabama Power, Georgia Power, and Mississippi Power and up to 14 years for 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 Units 8, 9, and 10 ($533 million at December 31, 2021) being amortized over remaining periods not exceeding 16 years (through 2037). Georgia Power: Net book values of Plant Hammond Units 1 through 4 and Plant Branch Units 3 and 4 (totaling $445 million at December 31, 2021) are being amortized over remaining periods of between two and 14 years (between 2023 and 2035) and the net book values of Plant Branch Unit 2, Plant McIntosh Unit 1, and Plant Mitchell Unit 3 (totaling $10 million at December 31, 2021) are being amortized through 2022. Mississippi Power: Represents net book value of certain environmental compliance projects associated with Plant Watson and Plant Greene County being amortized over a 10-year period through 2030. See "Mississippi Power – Environmental Compliance Overview Plan" herein for additional information. (d)Deferred income tax charges are recovered and deferred income tax credits are amortized over the related property lives, which may range up to 53 years for Alabama Power, 60 years for Georgia Power, 55 years for Mississippi Power, and 80 years for Southern Company Gas. See Note 10 for additional information. Included in the deferred income tax charges are amounts ($7 million and $4 million for Alabama Power and Georgia Power, respectively, at December 31, 2021) for the retiree Medicare drug subsidy, which are being recovered and amortized through 2027 and 2022 for Alabama Power and Georgia Power, respectively. 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 are being recovered and amortized ratably over the related property lives. Georgia Power: Related amounts at December 31, 2021 include $145 million of deferred income tax assets related to CWIP for Plant Vogtle Units 3 and 4 and approximately $220 million of deferred income tax liabilities. The recovery of deferred income tax assets related to CWIP for Plant Vogtle Units 3 and 4 is expected to be determined in a future regulatory proceeding. Effective January 1, 2020, the deferred income tax liabilities are being amortized through 2022. Mississippi Power: Related amounts at December 31, 2021 include $46 million of retail deferred income tax liabilities generally being amortized over three years (through 2023). See "Mississippi Power – 2019 Base Rate Case" herein for additional information. Southern Company Gas: Related amounts at December 31, 2021 include $3 million of deferred income tax liabilities 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 or returned within eight years. Recovery periods could change based on several factors including changes in cost estimates, load forecasts, and timing of rate adjustments. 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, 2021, $24 million is being amortized over a three-year period through 2023 and the remaining $25 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 four 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. The significant change during 2021 was primarily driven by an increase in the cost of gas purchased in February 2021 resulting from Winter Storm Uri. (f)Georgia Power is recovering $12 million annually for environmental remediation under the 2019 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. (g)Recovered over either the remaining life of the original issue or, if refinanced, over the remaining life of the new issue. At December 31, 2021, the remaining amortization periods do not exceed 26 years for Alabama Power, 31 years for Georgia Power, 20 years for Mississippi Power, and six years for Southern Company Gas. (h)Recorded as earned by employees and recovered as paid, generally within one year. Includes both vacation and banked holiday pay, if applicable. (i)Will be amortized concurrently with the effective date of Alabama Power's next depreciation study, which is expected to occur no later than 2023. (j)Georgia Power is recovering approximately $213 million annually for storm damage under the 2019 ARP. See "Georgia Power – Storm Damage Recovery" herein for additional information. Mississippi Power's balance represents deferred storm costs associated with Hurricanes Ida and Zeta to be recovered through PEP over a period to be determined in Mississippi Power's 2022 PEP proceeding. See "Mississippi Power – System Restoration Rider" herein for additional information. Also see Note 1 under "Storm Damage Reserves" for additional information. (k)Recovered over the remaining lives of the original debt issuances at acquisition, which range up to 17 years at December 31, 2021. (l)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. (m)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. See "Alabama Power – Software Accounting Order" herein for additional information. For Georgia Power, the recovery period will be determined in its next base rate case. For Southern Company Gas, costs will be amortized ratably beginning in July 2022 over the life of the related software, which ranges up to 10 years. (n)Includes $44 million of regulatory assets and $9 million of regulatory liabilities at December 31, 2021. The retail portion includes $33 million of regulatory assets and $9 million of regulatory liabilities that are expected to be fully amortized by 2023 and 2024, respectively. The wholesale portion includes $11 million of regulatory assets that are expected to be fully amortized by 2029. (o)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, 2021, consists of the $19 million retail portion, which is being amortized over the remaining life of the units through 2041, and the $9 million wholesale portion, which is expected to be amortized over a period to be determined in a future wholesale rate filing. (p)Except as otherwise noted, comprised of numerous immaterial components with remaining amortization periods generally not exceeding 23 years for Alabama Power, 10 years for Georgia Power, six years for Mississippi Power, and 20 years for Southern Company Gas at December 31, 2021. Balances at December 31, 2021 and 2020 include deferred COVID-19 costs (except for Alabama Power), as discussed further under "Deferral of Incremental COVID-19 Costs" for each applicable Registrant herein. (q)Primarily includes approximately $181 million and $50 million at December 31, 2021 and 2020, respectively, for Alabama Power and $5 million at December 31, 2021 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. (r)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 three years for Mississippi Power. Immaterial amounts at December 31, 2020 are included in other regulatory assets and liabilities. (s)Amortized as related expenses are incurred. See "Alabama Power – Rate NDR" and "Mississippi Power – System Restoration Rider" herein for additional information. (t)Comprised of numerous immaterial components with remaining amortization periods generally not exceeding 16 years for Alabama Power, 11 years for Georgia Power, three years for Mississippi Power, and 20 years for Southern Company Gas at December 31, 2021. (u)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 composed 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, 2021 |  | December 31, 2020
| (in millions)
Atlanta Gas Light | $ | 47 |  |  | $ | 59 |
Virginia Natural Gas | 10 |  |  | 10 |
Chattanooga Gas | 4 |  |  | 2 |
Nicor Gas | — |  |  | 3 |
Total | $ | 61 |  |  | $ | 74 |
Schedule of regulatory liabilities | Details of regulatory assets and (liabilities) reflected in the balance sheets at December 31, 2021 and 2020 are provided in the following tables:
| Southern Company | Alabama Power | Georgia Power | Mississippi Power | Southern Company Gas
| (in millions)
At December 31, 2021 |  |  |  |  |
AROs(a)(u) | $ | 5,685 |  | $ | 1,576 |  | $ | 3,866 |  | $ | 236 |  | $ | — |
Retiree benefit plans(b)(u) | 2,998 |  | 747 |  | 962 |  | 145 |  | 95 |
Remaining net book value of retired assets(c) | 1,050 |  | 574 |  | 455 |  | 21 |  | — |
Deferred income tax charges(d) | 829 |  | 240 |  | 555 |  | 31 |  | — |
Under recovered regulatory clause revenues(e) | 806 |  | 225 |  | — |  | 49 |  | 532 |
Environmental remediation(f)(u) | 302 |  | — |  | 35 |  | — |  | 267 |
Loss on reacquired debt(g) | 281 |  | 42 |  | 231 |  | 6 |  | 2 |
Vacation pay(h)(u) | 207 |  | 81 |  | 102 |  | 10 |  | 14 |
Regulatory clauses(i) | 142 |  | 142 |  | — |  | — |  | — |
Storm damage(j) | 97 |  | — |  | 48 |  | 49 |  | — |
Long-term debt fair value adjustment(k) | 79 |  | — |  | — |  | — |  | 79 |
Nuclear outage(l) | 75 |  | 41 |  | 34 |  | — |  | — |
Software and cloud computing costs(m) | 73 |  | 35 |  | 33 |  | — |  | 5 |
Kemper County energy facility assets, net(n) | 35 |  | — |  | — |  | 35 |  | — |
Plant Daniel Units 3 and 4(o) | 28 |  | — |  | — |  | 28 |  | — |
Other regulatory assets(p) | 168 |  | 38 |  | 29 |  | 7 |  | 94 |
Deferred income tax credits(d) | (5,636) |  | (1,968) |  | (2,537) |  | (288) |  | (816) |
Other cost of removal obligations(a) | (1,826) |  | (192) |  | 278 |  | (195) |  | (1,683) |
Customer refunds(q) | (189) |  | (181) |  | (8) |  | — |  | — |
Fuel-hedging (realized and unrealized) gains(r) | (176) |  | (50) |  | (72) |  | (54) |  | — |
Storm/property damage reserves(s) | (133) |  | (103) |  | — |  | (30) |  | — |
Over recovered regulatory clause revenues(e) | (63) |  | (1) |  | (59) |  | — |  | (3) |
Other regulatory liabilities(t) | (121) |  | (29) |  | (24) |  | (4) |  | (57) |
Total regulatory assets (liabilities), net | $ | 4,711 |  | $ | 1,217 |  | $ | 3,928 |  | $ | 46 |  | $ | (1,471) |
| Southern Company | Alabama Power | Georgia Power | Mississippi Power | Southern Company Gas
| (in millions)
At December 31, 2020 |  |  |  |  |
AROs(a)(u) | $ | 5,147 |  | $ | 1,470 |  | $ | 3,457 |  | $ | 212 |  | $ | — |
Retiree benefit plans(b)(u) | 4,958 |  | 1,265 |  | 1,647 |  | 238 |  | 187 |
Remaining net book value of retired assets(c) | 1,183 |  | 632 |  | 527 |  | 24 |  | — |
Deferred income tax charges(d) | 801 |  | 235 |  | 531 |  | 32 |  | — |
Environmental remediation(f)(u) | 310 |  | — |  | 41 |  | — |  | 269 |
Loss on reacquired debt(g) | 304 |  | 47 |  | 248 |  | 6 |  | 3 |
Storm damage(j) | 262 |  | — |  | 262 |  | — |  | — |
Vacation pay(h)(u) | 207 |  | 80 |  | 104 |  | 10 |  | 13 |
Under recovered regulatory clause revenues(e) | 185 |  | 58 |  | — |  | 52 |  | 75 |
Regulatory clauses(i) | 142 |  | 142 |  | — |  | — |  | — |
Nuclear outage(l) | 101 |  | 61 |  | 40 |  | — |  | — |
Long-term debt fair value adjustment(k) | 92 |  | — |  | — |  | — |  | 92 |
Kemper County energy facility assets, net(n) | 50 |  | — |  | — |  | 50 |  | — |
Plant Daniel Units 3 and 4(o) | 32 |  | — |  | — |  | 32 |  | — |
Software and cloud computing costs(m) | 31 |  | 17 |  | 12 |  | — |  | 2 |
Other regulatory assets(p) | 174 |  | 35 |  | 56 |  | 4 |  | 79 |
Deferred income tax credits(d) | (6,016) |  | (2,016) |  | (2,805) |  | (320) |  | (847) |
Other cost of removal obligations(a) | (1,999) |  | (335) |  | 212 |  | (194) |  | (1,649) |
Over recovered regulatory clause revenues(e) | (185) |  | (46) |  | (44) |  | — |  | (95) |
Storm/property damage reserves(s) | (81) |  | (77) |  | — |  | (4) |  | — |
Customer refunds(q) | (56) |  | (50) |  | (6) |  | — |  | — |
Other regulatory liabilities(t) | (149) |  | (37) |  | (30) |  | (6) |  | (54) |
Total regulatory assets (liabilities), net | $ | 5,493 |  | $ | 1,481 |  | $ | 4,252 |  | $ | 136 |  | $ | (1,925) |
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 53 years for Alabama Power, 60 years for Georgia Power, 55 years for Mississippi Power, and 80 years for Southern Company Gas. AROs and cost of removal obligations will be settled and trued up following completion of the related activities. Effective January 1, 2020, Georgia Power is recovering CCR AROs, including past under recovered costs and estimated annual compliance costs, over three-year periods ending December 31, 2022, 2023, and 2024 through its ECCR tariff, as discussed further under "Georgia Power – Rate Plans" herein. See Note 6 for additional information on AROs. (b)Recovered and amortized over the average remaining service period, which may range up to 13 years for Alabama Power, Georgia Power, and Mississippi Power and up to 14 years for 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 Units 8, 9, and 10 ($533 million at December 31, 2021) being amortized over remaining periods not exceeding 16 years (through 2037). Georgia Power: Net book values of Plant Hammond Units 1 through 4 and Plant Branch Units 3 and 4 (totaling $445 million at December 31, 2021) are being amortized over remaining periods of between two and 14 years (between 2023 and 2035) and the net book values of Plant Branch Unit 2, Plant McIntosh Unit 1, and Plant Mitchell Unit 3 (totaling $10 million at December 31, 2021) are being amortized through 2022. Mississippi Power: Represents net book value of certain environmental compliance projects associated with Plant Watson and Plant Greene County being amortized over a 10-year period through 2030. See "Mississippi Power – Environmental Compliance Overview Plan" herein for additional information. (d)Deferred income tax charges are recovered and deferred income tax credits are amortized over the related property lives, which may range up to 53 years for Alabama Power, 60 years for Georgia Power, 55 years for Mississippi Power, and 80 years for Southern Company Gas. See Note 10 for additional information. Included in the deferred income tax charges are amounts ($7 million and $4 million for Alabama Power and Georgia Power, respectively, at December 31, 2021) for the retiree Medicare drug subsidy, which are being recovered and amortized through 2027 and 2022 for Alabama Power and Georgia Power, respectively. 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 are being recovered and amortized ratably over the related property lives. Georgia Power: Related amounts at December 31, 2021 include $145 million of deferred income tax assets related to CWIP for Plant Vogtle Units 3 and 4 and approximately $220 million of deferred income tax liabilities. The recovery of deferred income tax assets related to CWIP for Plant Vogtle Units 3 and 4 is expected to be determined in a future regulatory proceeding. Effective January 1, 2020, the deferred income tax liabilities are being amortized through 2022. Mississippi Power: Related amounts at December 31, 2021 include $46 million of retail deferred income tax liabilities generally being amortized over three years (through 2023). See "Mississippi Power – 2019 Base Rate Case" herein for additional information. Southern Company Gas: Related amounts at December 31, 2021 include $3 million of deferred income tax liabilities 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 or returned within eight years. Recovery periods could change based on several factors including changes in cost estimates, load forecasts, and timing of rate adjustments. 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, 2021, $24 million is being amortized over a three-year period through 2023 and the remaining $25 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 four 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. The significant change during 2021 was primarily driven by an increase in the cost of gas purchased in February 2021 resulting from Winter Storm Uri. (f)Georgia Power is recovering $12 million annually for environmental remediation under the 2019 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. (g)Recovered over either the remaining life of the original issue or, if refinanced, over the remaining life of the new issue. At December 31, 2021, the remaining amortization periods do not exceed 26 years for Alabama Power, 31 years for Georgia Power, 20 years for Mississippi Power, and six years for Southern Company Gas. (h)Recorded as earned by employees and recovered as paid, generally within one year. Includes both vacation and banked holiday pay, if applicable. (i)Will be amortized concurrently with the effective date of Alabama Power's next depreciation study, which is expected to occur no later than 2023. (j)Georgia Power is recovering approximately $213 million annually for storm damage under the 2019 ARP. See "Georgia Power – Storm Damage Recovery" herein for additional information. Mississippi Power's balance represents deferred storm costs associated with Hurricanes Ida and Zeta to be recovered through PEP over a period to be determined in Mississippi Power's 2022 PEP proceeding. See "Mississippi Power – System Restoration Rider" herein for additional information. Also see Note 1 under "Storm Damage Reserves" for additional information. (k)Recovered over the remaining lives of the original debt issuances at acquisition, which range up to 17 years at December 31, 2021. (l)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. (m)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. See "Alabama Power – Software Accounting Order" herein for additional information. For Georgia Power, the recovery period will be determined in its next base rate case. For Southern Company Gas, costs will be amortized ratably beginning in July 2022 over the life of the related software, which ranges up to 10 years. (n)Includes $44 million of regulatory assets and $9 million of regulatory liabilities at December 31, 2021. The retail portion includes $33 million of regulatory assets and $9 million of regulatory liabilities that are expected to be fully amortized by 2023 and 2024, respectively. The wholesale portion includes $11 million of regulatory assets that are expected to be fully amortized by 2029. (o)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, 2021, consists of the $19 million retail portion, which is being amortized over the remaining life of the units through 2041, and the $9 million wholesale portion, which is expected to be amortized over a period to be determined in a future wholesale rate filing. (p)Except as otherwise noted, comprised of numerous immaterial components with remaining amortization periods generally not exceeding 23 years for Alabama Power, 10 years for Georgia Power, six years for Mississippi Power, and 20 years for Southern Company Gas at December 31, 2021. Balances at December 31, 2021 and 2020 include deferred COVID-19 costs (except for Alabama Power), as discussed further under "Deferral of Incremental COVID-19 Costs" for each applicable Registrant herein. (q)Primarily includes approximately $181 million and $50 million at December 31, 2021 and 2020, respectively, for Alabama Power and $5 million at December 31, 2021 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. (r)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 three years for Mississippi Power. Immaterial amounts at December 31, 2020 are included in other regulatory assets and liabilities. (s)Amortized as related expenses are incurred. See "Alabama Power – Rate NDR" and "Mississippi Power – System Restoration Rider" herein for additional information. (t)Comprised of numerous immaterial components with remaining amortization periods generally not exceeding 16 years for Alabama Power, 11 years for Georgia Power, three years for Mississippi Power, and 20 years for Southern Company Gas at December 31, 2021. (u)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 table below:
Tariff | 2020 |  | 2021 |  | 2022
| (in millions)
Traditional base | $ | — |  |  | $ | 120 |  |  | $ | 192 |
ECCR(*) | 318 |  |  | 2 |  |  | (12) |
DSM | 12 |  |  | (15) |  |  | (25) |
MFF | 12 |  |  | 4 |  |  | 2 |
Total | $ | 342 |  |  | $ | 111 |  |  | $ | 157 |
(*) Effective January 1, 2020, CCR AROs are being recovered through the ECCR tariff. 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(a) | 9.75% |  | 10.25% |  | 9.50% |  | 9.80%
Weather normalization mechanisms(b) |  |  |  |  | ü |  | ü
Decoupled, including straight-fixed-variable rates(c) | ü |  | ü |  | ü |  |
Regulatory infrastructure program rates(d) | ü |  | ü |  | ü |  | ü
Bad debt rider(e) | ü |  |  |  | ü |  | ü
Energy efficiency plan(f) | ü |  |  |  | ü |  |
Annual base rate adjustment mechanism(g) |  |  | ü |  |  |  | ü
Year of last base rate case decision(h) | 2021 |  | 2019 |  | 2021 |  | 2018
(a)Represents the authorized ROE at December 31, 2021. (b)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. (c)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. (d)Programs that update or expand distribution systems and LNG facilities. Atlanta Gas Light's infrastructure program, System Reinforcement Rider, is effective for 2022 through 2024. See "Rate Proceedings – Atlanta Gas Light" herein for additional information. Chattanooga Gas' pipeline replacement program costs are recovered through its annual base rate review mechanism. (e)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. (f)Recovery of costs associated with plans to achieve specified energy savings goals. (g)Regulatory mechanism allowing annual adjustments to base rates up or down based on authorized ROE and/or ROE range. (h)Annual GRAM filing required at Atlanta Gas Light. The following table and discussions provide updates on the infrastructure replacement programs and capital projects at the natural gas distribution utilities at December 31, 2021. 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 |  | Expenditures in 2021 |  | 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(*) |  |  |  | Rider |  | $ | 408 |  |  | $ | 2,508 |  |  | 1,153 |  |  | 1,394 |  |  | 9 |  | 2023
Virginia Natural Gas |  | Steps to Advance Virginia's Energy (SAVE) |  |  |  | Rider |  | 51 |  |  | 342 |  |  | 470 |  |  | 640 |  |  | 13 |  | 2024
Atlanta Gas Light |  | System Reinforcement Rider |  |  |  | Rider |  | — |  |  | — |  |  | N/A |  | N/A |  | 3 |  | 2024
Chattanooga Gas |  | Pipeline Replacement Program |  |  |  | Rate Base |  | 2 |  |  | 2 |  |  | 5 |  |  | 73 |  |  | 7 |  | 2027
Total |  |  |  |  |  |  |  | $ | 461 |  |  | $ | 2,852 |  |  | 1,628 |  |  | 2,107 |  |  |  |  |
(*)Includes replacement of pipes, compressors, and transmission mains along with other improvements such as new meters. Scope of program miles is an estimate and subject to change. Recovery of program costs is described under "Nicor Gas" herein.
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 end of the first quarter 2023 and the fourth quarter 2023, respectively, is as follows:
| (in millions)
Base project capital cost forecast(a)(b) | $ | 10,251 |
Construction contingency estimate | 150 |
Total project capital cost forecast(a)(b) | 10,401 |
Net investment at December 31, 2021(b) | (8,442) |
Remaining estimate to complete | $ | 1,959 |
(a)Includes approximately $590 million of costs that are not shared with the other Vogtle Owners and approximately $440 million of incremental costs under the cost-sharing and tender provisions of the joint ownership agreements described below. Excludes financing costs expected to be capitalized through AFUDC of approximately $375 million, of which $195 million had been accrued through December 31, 2021. (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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