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Segments Of Business (Tables) | 9 Months Ended
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Sep. 30, 2025
Segment Reporting Information [Line Items] |
Schedule Of Segments Of Business | Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):
| Utility |  |  |  |
|  |  |  |  | Total |  |  |  | Alliant
|  |  |  |  | Reportable |  |  |  | Energy
Three Months Ended September 30, 2025 | IPL |  | WPL |  | Segments |  | Other |  | Consolidated
Electric utility revenues | $608 |  | $516 |  | $1,124 |  | N/A |  | $1,124
Gas utility revenues | 27 |  | 24 |  | 51 |  | N/A |  | 51
Other revenues | 12 |  | — |  | 12 |  | $23 |  | 35
Total revenues | 647 |  | 540 |  | 1,187 |  | 23 |  | 1,210
Electric production fuel and purchased power expense | 106 |  | 133 |  | 239 |  | N/A |  | 239
Electric transmission service expense | 115 |  | 51 |  | 166 |  | N/A |  | 166
Cost of gas sold expense | 7 |  | 5 |  | 12 |  | N/A |  | 12
Other operation and maintenance expense | 108 |  | 84 |  | 192 |  | 12 |  | 204
Other segment items: |  |  |  |  |  |  |  |  |
Depreciation and amortization expense | 116 |  | 92 |  | 208 |  | 3 |  | 211
Interest expense | 54 |  | 43 |  | 97 |  | 31 |  | 128
Equity income from unconsolidated investments, net | — |  | (1) |  | (1) |  | (17) |  | (18)
Income tax expense (benefit) | (21) |  | 1 |  | (20) |  | 2 |  | (18)
Other (a) | (3) |  | 9 |  | 6 |  | (1) |  | 5
Net income (loss) | 165 |  | 123 |  | 288 |  | (7) |  | 281
Total assets (as of September 30, 2025) | 12,433 |  | 10,331 |  | 22,764 |  | 1,863 |  | 24,627
Investments in equity method subsidiaries (as of September 30, 2025) | 5 |  | 19 |  | 24 |  | 644 |  | 668
Construction and acquisition expenditures | 348 |  | 163 |  | 511 |  | 72 |  | 583
| Utility |  |  |  |
|  |  |  |  | Total |  |  |  | Alliant
Three Months Ended September 30, 2024 (amounts may not foot due to rounding) |  |  |  |  | Reportable |  |  |  | Energy
IPL |  | WPL |  | Segments |  | Other |  | Consolidated
Electric utility revenues | $523 |  | $476 |  | $999 |  | N/A |  | $999
Gas utility revenues | 27 |  | 22 |  | 49 |  | N/A |  | 49
Other revenues | 11 |  | 1 |  | 12 |  | $21 |  | 33
Total revenues | 561 |  | 499 |  | 1,060 |  | 21 |  | 1,081
Electric production fuel and purchased power expense | 79 |  | 112 |  | 191 |  | N/A |  | 192
Electric transmission service expense | 115 |  | 49 |  | 164 |  | N/A |  | 165
Cost of gas sold expense | 8 |  | 5 |  | 13 |  | N/A |  | 13
Other operation and maintenance expense | 96 |  | 72 |  | 168 |  | 6 |  | 174
Other segment items: |  |  |  |  |  |  |  |  |
Depreciation and amortization expense | 100 |  | 91 |  | 191 |  | 4 |  | 195
Interest expense | 44 |  | 42 |  | 86 |  | 28 |  | 114
Equity income from unconsolidated investments, net | — |  | (1) |  | (1) |  | (13) |  | (14)
Income tax expense (benefit) | (68) |  | 4 |  | (64) |  | 2 |  | (62)
Other (a) | (3) |  | 11 |  | 8 |  | 3 |  | 9
Net income (loss) | 190 |  | 114 |  | 304 |  | (9) |  | 295
Total assets (as of September 30, 2024) | 11,680 |  | 9,938 |  | 21,618 |  | 1,211 |  | 22,829
Investments in equity method subsidiaries (as of September 30, 2024) | 5 |  | 17 |  | 22 |  | 594 |  | 616
Construction and acquisition expenditures | 202 |  | 208 |  | 410 |  | 64 |  | 474
| Utility |  |  |  |
|  |  |  |  | Total |  |  |  | Alliant
|  |  |  |  | Reportable |  |  |  | Energy
Nine Months Ended September 30, 2025 | IPL |  | WPL |  | Segments |  | Other |  | Consolidated
Electric utility revenues | $1,455 |  | $1,373 |  | $2,828 |  | N/A |  | $2,828
Gas utility revenues | 185 |  | 181 |  | 366 |  | N/A |  | 366
Other revenues | 36 |  | 1 |  | 37 |  | $67 |  | 104
Total revenues | 1,676 |  | 1,555 |  | 3,231 |  | 67 |  | 3,298
Electric production fuel and purchased power expense | 213 |  | 351 |  | 564 |  | N/A |  | 564
Electric transmission service expense | 322 |  | 152 |  | 474 |  | N/A |  | 474
Cost of gas sold expense | 89 |  | 91 |  | 180 |  | N/A |  | 180
Other operation and maintenance expense | 275 |  | 222 |  | 497 |  | 33 |  | 530
Other segment items: |  |  |  |  |  |  |  |  |
Depreciation and amortization expense | 346 |  | 275 |  | 621 |  | 10 |  | 631
Interest expense | 154 |  | 129 |  | 283 |  | 89 |  | 372
Equity income from unconsolidated investments, net | — |  | (1) |  | (1) |  | (40) |  | (41)
Income tax benefit | (98) |  | (9) |  | (107) |  | (2) |  | (109)
Other (a) | 1 |  | 24 |  | 25 |  | 4 |  | 29
Net income (loss) | 374 |  | 321 |  | 695 |  | (27) |  | 668
Construction and acquisition expenditures | 976 |  | 511 |  | 1,487 |  | 161 |  | 1,648
| Utility |  |  |  |
|  |  |  |  | Total |  |  |  | Alliant
Nine Months Ended September 30, 2024 (amounts may not foot due to rounding) |  |  |  |  | Reportable |  |  |  | Energy
IPL |  | WPL |  | Segments |  | Other |  | Consolidated
Electric utility revenues | $1,318 |  | $1,261 |  | $2,579 |  | N/A |  | $2,579
Gas utility revenues | 175 |  | 147 |  | 322 |  | N/A |  | 322
Other revenues | 34 |  | 2 |  | 36 |  | $68 |  | 104
Total revenues | 1,527 |  | 1,410 |  | 2,937 |  | 68 |  | 3,005
Electric production fuel and purchased power expense | 195 |  | 298 |  | 493 |  | N/A |  | 493
Electric transmission service expense | 317 |  | 148 |  | 465 |  | N/A |  | 464
Cost of gas sold expense | 85 |  | 67 |  | 152 |  | N/A |  | 152
Asset valuation charge for IPL’s Lansing Generating Station | 60 |  | — |  | 60 |  | N/A |  | 60
Other operation and maintenance expense | 281 |  | 200 |  | 481 |  | 29 |  | 510
Other segment items: |  |  |  |  |  |  |  |  |
Depreciation and amortization expense | 294 |  | 269 |  | 563 |  | 8 |  | 571
Interest expense | 128 |  | 124 |  | 252 |  | 77 |  | 329
Equity income from unconsolidated investments, net | — |  | (2) |  | (2) |  | (42) |  | (44)
Income tax expense (benefit) | (112) |  | 13 |  | (99) |  | (5) |  | (104)
Other (a) | 7 |  | 23 |  | 30 |  | 3 |  | 34
Net income (loss) | 272 |  | 270 |  | 542 |  | (2) |  | 540
Construction and acquisition expenditures | 702 |  | 578 |  | 1,280 |  | 154 |  | 1,434
(a)Other segment items for each reportable segment include allowance for funds used during construction, taxes other than income taxes, interest income, and other miscellaneous income and deductions.
IPL [Member] |
Segment Reporting Information [Line Items] |
Schedule Of Segments Of Business | Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):
| Utility |  |  |  |
|  |  |  |  | Total |  |  |  | Alliant
|  |  |  |  | Reportable |  |  |  | Energy
Three Months Ended September 30, 2025 | IPL |  | WPL |  | Segments |  | Other |  | Consolidated
Electric utility revenues | $608 |  | $516 |  | $1,124 |  | N/A |  | $1,124
Gas utility revenues | 27 |  | 24 |  | 51 |  | N/A |  | 51
Other revenues | 12 |  | — |  | 12 |  | $23 |  | 35
Total revenues | 647 |  | 540 |  | 1,187 |  | 23 |  | 1,210
Electric production fuel and purchased power expense | 106 |  | 133 |  | 239 |  | N/A |  | 239
Electric transmission service expense | 115 |  | 51 |  | 166 |  | N/A |  | 166
Cost of gas sold expense | 7 |  | 5 |  | 12 |  | N/A |  | 12
Other operation and maintenance expense | 108 |  | 84 |  | 192 |  | 12 |  | 204
Other segment items: |  |  |  |  |  |  |  |  |
Depreciation and amortization expense | 116 |  | 92 |  | 208 |  | 3 |  | 211
Interest expense | 54 |  | 43 |  | 97 |  | 31 |  | 128
Equity income from unconsolidated investments, net | — |  | (1) |  | (1) |  | (17) |  | (18)
Income tax expense (benefit) | (21) |  | 1 |  | (20) |  | 2 |  | (18)
Other (a) | (3) |  | 9 |  | 6 |  | (1) |  | 5
Net income (loss) | 165 |  | 123 |  | 288 |  | (7) |  | 281
Total assets (as of September 30, 2025) | 12,433 |  | 10,331 |  | 22,764 |  | 1,863 |  | 24,627
Investments in equity method subsidiaries (as of September 30, 2025) | 5 |  | 19 |  | 24 |  | 644 |  | 668
Construction and acquisition expenditures | 348 |  | 163 |  | 511 |  | 72 |  | 583
| Utility |  |  |  |
|  |  |  |  | Total |  |  |  | Alliant
Three Months Ended September 30, 2024 (amounts may not foot due to rounding) |  |  |  |  | Reportable |  |  |  | Energy
IPL |  | WPL |  | Segments |  | Other |  | Consolidated
Electric utility revenues | $523 |  | $476 |  | $999 |  | N/A |  | $999
Gas utility revenues | 27 |  | 22 |  | 49 |  | N/A |  | 49
Other revenues | 11 |  | 1 |  | 12 |  | $21 |  | 33
Total revenues | 561 |  | 499 |  | 1,060 |  | 21 |  | 1,081
Electric production fuel and purchased power expense | 79 |  | 112 |  | 191 |  | N/A |  | 192
Electric transmission service expense | 115 |  | 49 |  | 164 |  | N/A |  | 165
Cost of gas sold expense | 8 |  | 5 |  | 13 |  | N/A |  | 13
Other operation and maintenance expense | 96 |  | 72 |  | 168 |  | 6 |  | 174
Other segment items: |  |  |  |  |  |  |  |  |
Depreciation and amortization expense | 100 |  | 91 |  | 191 |  | 4 |  | 195
Interest expense | 44 |  | 42 |  | 86 |  | 28 |  | 114
Equity income from unconsolidated investments, net | — |  | (1) |  | (1) |  | (13) |  | (14)
Income tax expense (benefit) | (68) |  | 4 |  | (64) |  | 2 |  | (62)
Other (a) | (3) |  | 11 |  | 8 |  | 3 |  | 9
Net income (loss) | 190 |  | 114 |  | 304 |  | (9) |  | 295
Total assets (as of September 30, 2024) | 11,680 |  | 9,938 |  | 21,618 |  | 1,211 |  | 22,829
Investments in equity method subsidiaries (as of September 30, 2024) | 5 |  | 17 |  | 22 |  | 594 |  | 616
Construction and acquisition expenditures | 202 |  | 208 |  | 410 |  | 64 |  | 474
| Utility |  |  |  |
|  |  |  |  | Total |  |  |  | Alliant
|  |  |  |  | Reportable |  |  |  | Energy
Nine Months Ended September 30, 2025 | IPL |  | WPL |  | Segments |  | Other |  | Consolidated
Electric utility revenues | $1,455 |  | $1,373 |  | $2,828 |  | N/A |  | $2,828
Gas utility revenues | 185 |  | 181 |  | 366 |  | N/A |  | 366
Other revenues | 36 |  | 1 |  | 37 |  | $67 |  | 104
Total revenues | 1,676 |  | 1,555 |  | 3,231 |  | 67 |  | 3,298
Electric production fuel and purchased power expense | 213 |  | 351 |  | 564 |  | N/A |  | 564
Electric transmission service expense | 322 |  | 152 |  | 474 |  | N/A |  | 474
Cost of gas sold expense | 89 |  | 91 |  | 180 |  | N/A |  | 180
Other operation and maintenance expense | 275 |  | 222 |  | 497 |  | 33 |  | 530
Other segment items: |  |  |  |  |  |  |  |  |
Depreciation and amortization expense | 346 |  | 275 |  | 621 |  | 10 |  | 631
Interest expense | 154 |  | 129 |  | 283 |  | 89 |  | 372
Equity income from unconsolidated investments, net | — |  | (1) |  | (1) |  | (40) |  | (41)
Income tax benefit | (98) |  | (9) |  | (107) |  | (2) |  | (109)
Other (a) | 1 |  | 24 |  | 25 |  | 4 |  | 29
Net income (loss) | 374 |  | 321 |  | 695 |  | (27) |  | 668
Construction and acquisition expenditures | 976 |  | 511 |  | 1,487 |  | 161 |  | 1,648
| Utility |  |  |  |
|  |  |  |  | Total |  |  |  | Alliant
Nine Months Ended September 30, 2024 (amounts may not foot due to rounding) |  |  |  |  | Reportable |  |  |  | Energy
IPL |  | WPL |  | Segments |  | Other |  | Consolidated
Electric utility revenues | $1,318 |  | $1,261 |  | $2,579 |  | N/A |  | $2,579
Gas utility revenues | 175 |  | 147 |  | 322 |  | N/A |  | 322
Other revenues | 34 |  | 2 |  | 36 |  | $68 |  | 104
Total revenues | 1,527 |  | 1,410 |  | 2,937 |  | 68 |  | 3,005
Electric production fuel and purchased power expense | 195 |  | 298 |  | 493 |  | N/A |  | 493
Electric transmission service expense | 317 |  | 148 |  | 465 |  | N/A |  | 464
Cost of gas sold expense | 85 |  | 67 |  | 152 |  | N/A |  | 152
Asset valuation charge for IPL’s Lansing Generating Station | 60 |  | — |  | 60 |  | N/A |  | 60
Other operation and maintenance expense | 281 |  | 200 |  | 481 |  | 29 |  | 510
Other segment items: |  |  |  |  |  |  |  |  |
Depreciation and amortization expense | 294 |  | 269 |  | 563 |  | 8 |  | 571
Interest expense | 128 |  | 124 |  | 252 |  | 77 |  | 329
Equity income from unconsolidated investments, net | — |  | (2) |  | (2) |  | (42) |  | (44)
Income tax expense (benefit) | (112) |  | 13 |  | (99) |  | (5) |  | (104)
Other (a) | 7 |  | 23 |  | 30 |  | 3 |  | 34
Net income (loss) | 272 |  | 270 |  | 542 |  | (2) |  | 540
Construction and acquisition expenditures | 702 |  | 578 |  | 1,280 |  | 154 |  | 1,434
(a)Other segment items for each reportable segment include allowance for funds used during construction, taxes other than income taxes, interest income, and other miscellaneous income and deductions.
WPL [Member] |
Segment Reporting Information [Line Items] |
Schedule Of Segments Of Business | Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):
| Utility |  |  |  |
|  |  |  |  | Total |  |  |  | Alliant
|  |  |  |  | Reportable |  |  |  | Energy
Three Months Ended September 30, 2025 | IPL |  | WPL |  | Segments |  | Other |  | Consolidated
Electric utility revenues | $608 |  | $516 |  | $1,124 |  | N/A |  | $1,124
Gas utility revenues | 27 |  | 24 |  | 51 |  | N/A |  | 51
Other revenues | 12 |  | — |  | 12 |  | $23 |  | 35
Total revenues | 647 |  | 540 |  | 1,187 |  | 23 |  | 1,210
Electric production fuel and purchased power expense | 106 |  | 133 |  | 239 |  | N/A |  | 239
Electric transmission service expense | 115 |  | 51 |  | 166 |  | N/A |  | 166
Cost of gas sold expense | 7 |  | 5 |  | 12 |  | N/A |  | 12
Other operation and maintenance expense | 108 |  | 84 |  | 192 |  | 12 |  | 204
Other segment items: |  |  |  |  |  |  |  |  |
Depreciation and amortization expense | 116 |  | 92 |  | 208 |  | 3 |  | 211
Interest expense | 54 |  | 43 |  | 97 |  | 31 |  | 128
Equity income from unconsolidated investments, net | — |  | (1) |  | (1) |  | (17) |  | (18)
Income tax expense (benefit) | (21) |  | 1 |  | (20) |  | 2 |  | (18)
Other (a) | (3) |  | 9 |  | 6 |  | (1) |  | 5
Net income (loss) | 165 |  | 123 |  | 288 |  | (7) |  | 281
Total assets (as of September 30, 2025) | 12,433 |  | 10,331 |  | 22,764 |  | 1,863 |  | 24,627
Investments in equity method subsidiaries (as of September 30, 2025) | 5 |  | 19 |  | 24 |  | 644 |  | 668
Construction and acquisition expenditures | 348 |  | 163 |  | 511 |  | 72 |  | 583
| Utility |  |  |  |
|  |  |  |  | Total |  |  |  | Alliant
Three Months Ended September 30, 2024 (amounts may not foot due to rounding) |  |  |  |  | Reportable |  |  |  | Energy
IPL |  | WPL |  | Segments |  | Other |  | Consolidated
Electric utility revenues | $523 |  | $476 |  | $999 |  | N/A |  | $999
Gas utility revenues | 27 |  | 22 |  | 49 |  | N/A |  | 49
Other revenues | 11 |  | 1 |  | 12 |  | $21 |  | 33
Total revenues | 561 |  | 499 |  | 1,060 |  | 21 |  | 1,081
Electric production fuel and purchased power expense | 79 |  | 112 |  | 191 |  | N/A |  | 192
Electric transmission service expense | 115 |  | 49 |  | 164 |  | N/A |  | 165
Cost of gas sold expense | 8 |  | 5 |  | 13 |  | N/A |  | 13
Other operation and maintenance expense | 96 |  | 72 |  | 168 |  | 6 |  | 174
Other segment items: |  |  |  |  |  |  |  |  |
Depreciation and amortization expense | 100 |  | 91 |  | 191 |  | 4 |  | 195
Interest expense | 44 |  | 42 |  | 86 |  | 28 |  | 114
Equity income from unconsolidated investments, net | — |  | (1) |  | (1) |  | (13) |  | (14)
Income tax expense (benefit) | (68) |  | 4 |  | (64) |  | 2 |  | (62)
Other (a) | (3) |  | 11 |  | 8 |  | 3 |  | 9
Net income (loss) | 190 |  | 114 |  | 304 |  | (9) |  | 295
Total assets (as of September 30, 2024) | 11,680 |  | 9,938 |  | 21,618 |  | 1,211 |  | 22,829
Investments in equity method subsidiaries (as of September 30, 2024) | 5 |  | 17 |  | 22 |  | 594 |  | 616
Construction and acquisition expenditures | 202 |  | 208 |  | 410 |  | 64 |  | 474
| Utility |  |  |  |
|  |  |  |  | Total |  |  |  | Alliant
|  |  |  |  | Reportable |  |  |  | Energy
Nine Months Ended September 30, 2025 | IPL |  | WPL |  | Segments |  | Other |  | Consolidated
Electric utility revenues | $1,455 |  | $1,373 |  | $2,828 |  | N/A |  | $2,828
Gas utility revenues | 185 |  | 181 |  | 366 |  | N/A |  | 366
Other revenues | 36 |  | 1 |  | 37 |  | $67 |  | 104
Total revenues | 1,676 |  | 1,555 |  | 3,231 |  | 67 |  | 3,298
Electric production fuel and purchased power expense | 213 |  | 351 |  | 564 |  | N/A |  | 564
Electric transmission service expense | 322 |  | 152 |  | 474 |  | N/A |  | 474
Cost of gas sold expense | 89 |  | 91 |  | 180 |  | N/A |  | 180
Other operation and maintenance expense | 275 |  | 222 |  | 497 |  | 33 |  | 530
Other segment items: |  |  |  |  |  |  |  |  |
Depreciation and amortization expense | 346 |  | 275 |  | 621 |  | 10 |  | 631
Interest expense | 154 |  | 129 |  | 283 |  | 89 |  | 372
Equity income from unconsolidated investments, net | — |  | (1) |  | (1) |  | (40) |  | (41)
Income tax benefit | (98) |  | (9) |  | (107) |  | (2) |  | (109)
Other (a) | 1 |  | 24 |  | 25 |  | 4 |  | 29
Net income (loss) | 374 |  | 321 |  | 695 |  | (27) |  | 668
Construction and acquisition expenditures | 976 |  | 511 |  | 1,487 |  | 161 |  | 1,648
| Utility |  |  |  |
|  |  |  |  | Total |  |  |  | Alliant
Nine Months Ended September 30, 2024 (amounts may not foot due to rounding) |  |  |  |  | Reportable |  |  |  | Energy
IPL |  | WPL |  | Segments |  | Other |  | Consolidated
Electric utility revenues | $1,318 |  | $1,261 |  | $2,579 |  | N/A |  | $2,579
Gas utility revenues | 175 |  | 147 |  | 322 |  | N/A |  | 322
Other revenues | 34 |  | 2 |  | 36 |  | $68 |  | 104
Total revenues | 1,527 |  | 1,410 |  | 2,937 |  | 68 |  | 3,005
Electric production fuel and purchased power expense | 195 |  | 298 |  | 493 |  | N/A |  | 493
Electric transmission service expense | 317 |  | 148 |  | 465 |  | N/A |  | 464
Cost of gas sold expense | 85 |  | 67 |  | 152 |  | N/A |  | 152
Asset valuation charge for IPL’s Lansing Generating Station | 60 |  | — |  | 60 |  | N/A |  | 60
Other operation and maintenance expense | 281 |  | 200 |  | 481 |  | 29 |  | 510
Other segment items: |  |  |  |  |  |  |  |  |
Depreciation and amortization expense | 294 |  | 269 |  | 563 |  | 8 |  | 571
Interest expense | 128 |  | 124 |  | 252 |  | 77 |  | 329
Equity income from unconsolidated investments, net | — |  | (2) |  | (2) |  | (42) |  | (44)
Income tax expense (benefit) | (112) |  | 13 |  | (99) |  | (5) |  | (104)
Other (a) | 7 |  | 23 |  | 30 |  | 3 |  | 34
Net income (loss) | 272 |  | 270 |  | 542 |  | (2) |  | 540
Construction and acquisition expenditures | 702 |  | 578 |  | 1,280 |  | 154 |  | 1,434
(a)Other segment items for each reportable segment include allowance for funds used during construction, taxes other than income taxes, interest income, and other miscellaneous income and deductions.

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- Definition Tabular disclosure of the profit or loss and total assets for each reportable segment. An entity discloses certain information on each reportable segment if the amounts (a) are included in the measure of segment profit or loss reviewed by the chief operating decision maker or (b) are otherwise regularly provided to the chief operating decision maker, even if not included in that measure of segment profit or loss. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 25 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482810/280-10-50-25 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 22 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482810/280-10-50-22 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 30 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482810/280-10-50-30 + Details
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