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RETIREMENT BENEFITS - Components of Accumulated OCI and Changes in Regulatory Assets (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Beginning balance | $ 32,234 | $ 31,759 | $ 29,039
Total other comprehensive income (loss) | 158 | (75) | (118)
Ending balance | 32,276 | 32,234 | 31,759
Pension and Other Postretirement Benefit Plans |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Beginning balance | (187) |  |
Total other comprehensive income (loss) | 111 |  |
Ending balance | (76) | (187) |
Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost | (2) | (3) |
Net loss | 102 | 248 |
Total AOCI | 100 | 245 |
Pension plans | Regulatory Assets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost | 11 | 11 |
Net loss | 2,790 | 4,610 |
Regulatory amortization | 0 | 0 |
Regulatory asset | 2,801 | 4,621 |
Pension plans | Pension and Other Postretirement Benefit Plans |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Beginning balance | 245 | 185 |
Reclassification adjustments | (17) | (14) |
Total other comprehensive income (loss) | (145) | 60 |
Ending balance | 100 | 245 | 185
Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Beginning balance | 4,621 | 3,993 |
Reclassification adjustments | (297) | (256) |
Total other comprehensive income (loss) | (1,820) | 628 |
Ending balance | 2,801 | 4,621 | 3,993
Pension plans | Net loss |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | 128 | (74) |
Reclassification adjustments | (17) | (14) |
Pension plans | Net loss | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | 1,523 | (884) |
Reclassification adjustments | (296) | (255) |
Pension plans | Change in prior service costs |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Reclassification adjustments |  | 0 |
Pension plans | Change in prior service costs | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Reclassification adjustments | (1) | (1) |
Pension plans | Amortization of regulatory assets | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Reclassification adjustments | 0 | 0 |
Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost | 1 | 1 |
Net loss | (1) | 7 |
Total AOCI | 0 | 8 |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Reclassification adjustments | 3 | 4 |
Other postretirement benefit plans | Regulatory Assets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost | 13 | 12 |
Net loss | (87) | 39 |
Regulatory amortization | 0 | 0 |
Regulatory asset |  | 51 |
Regulatory liabilities | (74) |  |
Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Beginning balance | 8 | 2 |
Total other comprehensive income (loss) | (8) | 6 |
Ending balance | 0 | 8 | 2
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 | 51 | 121 |
Reclassification adjustments | (5) | (5) |
Total other comprehensive income (loss) | (125) | (70) |
Ending balance | (74) | 51 | 121
Other postretirement benefit plans | Net loss |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | (11) | 2 |
Other postretirement benefit plans | Net loss | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | 120 | 65 |
Reclassification adjustments | (6) | (6) |
Other postretirement benefit plans | Change in prior service costs | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Reclassification adjustments | 1 | 1 |
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 | 9,810 | 8,955 | 7,477
Total other comprehensive income (loss) | 6 | 4 | 4
Ending balance | 10,713 | 9,810 | 8,955
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 | 5 | 5 |
Net loss | 804 | 1,281 |
Regulatory amortization | 0 | 0 |
Regulatory asset | 809 | 1,286 |
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 | 1,286 | 1,130 |
Reclassification adjustments | (83) | (72) |
Total other comprehensive income (loss) | (477) | 156 |
Ending balance | 809 | 1,286 | 1,130
Alabama Power | Pension plans | Net loss | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | 394 | (228) |
Reclassification adjustments | (82) | (71) |
Alabama Power | Pension plans | Change in prior service costs | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Reclassification adjustments | (1) | (1) |
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 | 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 | 3 |
Net loss | (65) | (24) |
Regulatory amortization | 0 | 0 |
Regulatory liabilities | (62) | (21) |
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 | (21) | 1 |
Reclassification adjustments | 0 | 0 |
Total other comprehensive income (loss) | (41) | (22) |
Ending balance | (62) | (21) | 1
Alabama Power | Other postretirement benefit plans | Net loss | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | 41 | 22 |
Reclassification adjustments | 0 | 0 |
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] |  |  |
Reclassification adjustments | 0 | 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 | 16,501 | 15,065 | 14,323
Total other comprehensive income (loss) | 6 | 4 | (42)
Ending balance | 17,234 | 16,501 | 15,065
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 | 8 | 9 |
Net loss | 963 | 1,589 |
Regulatory amortization | 0 | 0 |
Regulatory asset | 971 | 1,598 |
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 | 1,598 | 1,416 |
Reclassification adjustments | (100) | (87) |
Total other comprehensive income (loss) | (627) | 182 |
Ending balance | 971 | 1,598 | 1,416
Georgia Power | Pension plans | Net loss | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | 527 | (269) |
Reclassification adjustments | (99) | (86) |
Georgia Power | Pension plans | Change in prior service costs | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Reclassification adjustments | (1) | (1) |
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 | 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 | 5 | 5 |
Net loss | (15) | 42 |
Regulatory amortization | 0 | 0 |
Regulatory asset |  | 47 |
Regulatory liabilities | (10) |  |
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 | 47 | 96 |
Reclassification adjustments | (2) | (2) |
Total other comprehensive income (loss) | (57) | (49) |
Ending balance | (10) | 47 | 96
Georgia Power | Other postretirement benefit plans | Net loss | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | 55 | 47 |
Reclassification adjustments | (3) | (3) |
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] |  |  |
Reclassification adjustments | 1 | 1 |
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 | 1,742 | 1,652 | 1,609
Total other comprehensive income (loss) | 1 | 1 | 1
Ending balance | 1,867 | 1,742 | 1,652
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 | 1 | 2 |
Net loss | 145 | 233 |
Regulatory amortization | 0 | 0 |
Regulatory asset | 146 | 235 |
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 | 235 | 203 |
Reclassification adjustments | (15) | (13) |
Total other comprehensive income (loss) | (89) | 32 |
Ending balance | 146 | 235 | 203
Mississippi Power | Pension plans | Net loss | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | 74 | (45) |
Reclassification adjustments | (15) | (13) |
Mississippi Power | Pension plans | Change in prior service costs | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Reclassification adjustments | 0 | 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 | 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 | 1 | 0 |
Net loss | 0 | 5 |
Regulatory amortization | 0 | 0 |
Regulatory asset | 1 | 5 |
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 | 5 | 10 |
Reclassification adjustments | 0 | 0 |
Total other comprehensive income (loss) | (4) | (5) |
Ending balance | 1 | 5 | 10
Mississippi Power | Other postretirement benefit plans | Net loss | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | 4 | 5 |
Reclassification adjustments | 0 | 0 |
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] |  |  |
Reclassification adjustments | 0 | 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 | 6,631 | 6,622 | 7,284
Total other comprehensive income (loss) | 40 | (42) | (42)
Ending balance | 6,598 | 6,631 | 6,622
Southern Power | Pension and Other Postretirement Benefit Plans |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Beginning balance | (47) |  |
Total other comprehensive income (loss) | 18 |  |
Ending balance | (29) | (47) |
Southern Power | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost | 0 | 0 |
Net loss | 35 | 60 |
Total AOCI | 35 | 60 |
Southern Power | Pension plans | Pension and Other Postretirement Benefit Plans |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Beginning balance | 60 | 46 |
Reclassification adjustments | (3) | (2) |
Total other comprehensive income (loss) | (25) | 14 |
Ending balance | 35 | 60 | 46
Southern Power | Pension plans | Net loss |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | 22 | (16) |
Reclassification adjustments | (3) | (2) |
Southern Power | Pension plans | Change in prior service costs |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Reclassification adjustments |  | 0 |
Southern Power | Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost | 0 | 0 |
Net loss | 2 | 3 |
Total AOCI | 2 | 3 |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Reclassification adjustments | 0 | 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 | 3 | 2 |
Total other comprehensive income (loss) | (1) | 1 |
Ending balance | 2 | 3 | 2
Southern Power | Other postretirement benefit plans | Net loss |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | (1) | 1 |
Southern Company Gas |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Beginning balance | 9,767 | 9,506 | 8,570
Total other comprehensive income (loss) | 46 | (29) | (19)
Ending balance | 9,916 | 9,767 | 9,506
Southern Company Gas | Pension and Other Postretirement Benefit Plans |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Beginning balance | (2) |  |
Total other comprehensive income (loss) | 40 |  |
Ending balance | 38 | (2) |
Southern Company Gas | Pension plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost | (3) | (4) |
Net loss | (42) | 5 |
Total AOCI | (45) | 1 |
Regulatory asset | 210 | 224 |
Southern Company Gas | Pension plans | Regulatory Assets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost | (11) | (13) |
Net loss | 38 | 135 |
Regulatory amortization | 64 | 83 |
Regulatory asset | 91 | 205 |
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 | 1 | (14) |
Reclassification adjustments | 1 | 0 |
Total other comprehensive income (loss) | (46) | 15 |
Ending balance | (45) | 1 | (14)
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 | 205 | 172 |
Reclassification adjustments | (17) | (12) |
Total other comprehensive income (loss) | (114) | 33 |
Ending balance | 91 | 205 | 172
Southern Company Gas | Pension plans | Net loss |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | 47 | (15) |
Reclassification adjustments | 1 | (1) |
Southern Company Gas | Pension plans | Net loss | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | 97 | (45) |
Reclassification adjustments | (9) | (8) |
Southern Company Gas | Pension plans | Change in prior service costs |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Reclassification adjustments |  | 1 |
Southern Company Gas | Pension plans | Change in prior service costs | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Reclassification adjustments | 2 | 2 |
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 | (10) | (6) |
Southern Company Gas | Other postretirement benefit plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost | 1 | 1 |
Net loss | (6) | (1) |
Total AOCI | (5) | 0 |
Regulatory asset | 40 | 47 |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Reclassification adjustments | (5) | 4 |
Southern Company Gas | Other postretirement benefit plans | Regulatory Assets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Prior service cost | 1 | 1 |
Net loss | (51) | (49) |
Regulatory amortization | 16 | 25 |
Regulatory liabilities | (34) | (23) |
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 | 0 | (4) |
Total other comprehensive income (loss) | (5) | 4 |
Ending balance | (5) | 0 | (4)
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 | (23) | (11) |
Reclassification adjustments | (9) | (7) |
Total other comprehensive income (loss) | (11) | (12) |
Ending balance | (34) | (23) | $ (11)
Southern Company Gas | Other postretirement benefit plans | Net loss |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | 0 | 0 |
Southern Company Gas | Other postretirement benefit plans | Net loss | Regulatory Assets |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |
Other comprehensive (income) loss | 2 | 5 |
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] |  |  |
Reclassification adjustments | 0 | 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 | $ (9) | $ (7) |

X
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- Definition Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i-k) -URI http://asc.fasb.org/extlink&oid=124509347&loc=SL7669646-108580 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=124509347&loc=SL7669686-108580 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 + Details
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- Definition Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=124509347&loc=SL7669686-108580 + Details
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- Definition Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=124509347&loc=SL7669686-108580 + Details
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