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Rate And Regulatory Matters (Narrative-Federal) (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
May 31, 2020 | Dec. 31, 2024 | Sep. 30, 2026 | Sep. 30, 2025 | Sep. 30, 2024
Rate And Regulatory Matters [Line Items] |  |  |  |  |
Capital expenditures |  |  |  | $ 3,118 | $ 3,029
Current regulatory liabilities |  | $ 120 |  | 142 |
Forecast |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |
Capital expenditures |  |  | $ 1,300 |  |
Ameren Illinois Company |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |
Capital expenditures |  |  |  | 1,127 | $ 1,091
Current regulatory liabilities |  | $ 79 |  | 101 |
Midwest Independent Transmission System Operator, Inc | Final Rate Order |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |
Approved return on equity percentage | 10.02% | 9.98% |  |  |
Current regulatory liabilities |  |  |  | 7 |
Midwest Independent Transmission System Operator, Inc | Final Rate Order | Ameren Illinois Company |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |
Current regulatory liabilities |  |  |  | $ 4 |

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- Definition The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 13 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-13 + Details
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- Definition The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 405 -Name Accounting Standards Codification -Section 25 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477571/980-405-25-1 + Details
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