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REGULATORY MATTERS - GAS Infrastructure Replacement Programs and Capital Projects Schedule of QIP (Details) - Nicor Gas - USD ($) $ in Millions |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Nov. 16, 2023 | Dec. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2019
Commitments [Line Items] |  |  |  |
Disallowed |  | $ 69.0 |  |
Investing In Illinois Qualifying Infrastructure Plant |  |  |  |
Commitments [Line Items] |  |  |  |
Capital Investments |  |  | $ 3,228.0 |
Disallowed | $ 126.8 |  | 63.0 | $ 32.0
Investing In Illinois Qualifying Infrastructure Plant | Complete |  |  |  |
Commitments [Line Items] |  |  |  |
Capital Investments |  |  | 1,246.0 |
Disallowed |  |  | 0.0 |
Investing In Illinois Qualifying Infrastructure Plant | Complete(a) |  |  |  |
Commitments [Line Items] |  |  |  |
Capital Investments |  |  | 415.0 |
Disallowed |  |  | 32.0 |
Investing In Illinois Qualifying Infrastructure Plant | Filed March 2021 |  |  |  |
Commitments [Line Items] |  |  |  |
Capital Investments |  |  | 402.0 |
Disallowed |  |  |  |
Investing In Illinois Qualifying Infrastructure Plant | Filed March 2022 |  |  |  |
Commitments [Line Items] |  |  |  |
Capital Investments |  |  | 392.0 |
Disallowed |  |  |  |
Investing In Illinois Qualifying Infrastructure Plant | Filed March 2023 |  |  |  |
Commitments [Line Items] |  |  |  |
Capital Investments |  |  | 408.0 |
Disallowed |  |  | 6.0 |
Investing In Illinois Qualifying Infrastructure Plant | To be filed by March 20, 2024 |  |  |  |
Commitments [Line Items] |  |  |  |
Capital Investments |  |  | 365.0 |
Disallowed |  |  | $ 25.0 |

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