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Rate And Regulatory Matters (Narrative-Illinois) (Details) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2023 USD ($) | Sep. 30, 2023 USD ($) | Sep. 30, 2022 USD ($) | Sep. 30, 2023 USD ($) numberOfProposedPerformanceMetrics | Sep. 30, 2022 USD ($) | Dec. 31, 2027 USD ($) | Dec. 31, 2026 USD ($) | Dec. 31, 2025 USD ($) | Dec. 31, 2024 USD ($)
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Revenues |  | $ 2,060 | $ 2,306 | $ 5,882 | $ 5,911 |  |  |  |
Ameren Illinois Company |  |  |  |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Revenues |  | $ 783 | $ 904 | $ 2,663 | $ 2,697 |  |  |  |
Ameren Illinois Company | Maximum |  |  |  |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
ICC required RTO cost benefit study duration |  |  |  | 10 years |  |  |  |  |
Ameren Illinois Company | Minimum |  |  |  |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
ICC required RTO cost benefit study duration |  |  |  | 5 years |  |  |  |  |
Ameren Illinois Company | Electric Distribution |  |  |  |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Requested Return on Equity Adjustment |  |  |  | 0.24% |  |  |  |  |
Number of Performance Metrics | numberOfProposedPerformanceMetrics |  |  |  | 7 |  |  |  |  |
IETL | Ameren Illinois Company | Electric Distribution |  |  |  |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
ICC recommended return on equity percentage |  |  |  | 5.80% | 8.90% |  |  |  |
Public Utilities, Approved Equity Capital Structure, Percentage |  |  |  | 50.00% |  |  |  |  |
Amortization Period |  |  |  | 2 years |  |  |  |  |
Amortization Start Date |  |  |  | 1 year |  |  |  |  |
Multi-Year Rate Plan Reconciliation Cap |  |  |  | 105.00% |  |  |  |  |
IETL | Ameren Illinois Company | Electric Distribution | Forecast |  |  |  |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Multi-year rate plan requested revenue requirement |  |  |  |  |  | $ 1,556 | $ 1,480 | $ 1,385 | $ 1,289
Public Utilities, Requested Return on Equity, Percentage | 9.85% |  |  |  |  | 10.50% | 10.50% | 10.50% | 10.50%
Public Utilities, Requested Equity Capital Structure, Percentage | 52.00% |  |  |  |  | 54.03% | 54.02% | 53.97% | 53.99%
Rate Base |  |  |  |  |  | $ 5,200 | $ 4,900 | $ 4,600 | $ 4,300
Multi-year rate plan ICC staff recommended revenue requirement |  |  |  |  |  | $ 1,435 | $ 1,383 | $ 1,295 | $ 1,211
ICC recommended return on equity percentage |  |  |  |  |  | 8.90% | 8.90% | 8.90% | 8.90%
ICC staff recommended equity capital structure |  |  |  |  |  | 50.00% | 50.00% | 50.00% | 50.00%
ICC staff recommended rate base |  |  |  |  |  | $ 4,800 | $ 4,600 | $ 4,400 | $ 4,100
Multi-year rate plan ALJ proposed revenue requirement |  |  |  |  |  | $ 1,450 | $ 1,389 | $ 1,306 | $ 1,219
ALJ proposed return on equity percentage |  |  |  |  |  | 9.24% | 9.24% | 9.24% | 9.24%
ALJ proposed equity capital structure |  |  |  |  |  | 50.00% | 50.00% | 50.00% | 50.00%
ALJ proposed rate base |  |  |  |  |  | $ 4,800 | $ 4,600 | $ 4,400 | $ 4,100
Public Utilities, Requested Rate Increase (Decrease), Percentage |  |  |  |  |  |  | 50.00% |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  | $ 177
IETL | Ameren Illinois Company | Electric Distribution | Maximum | Forecast |  |  |  |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
ALJ proposed equity capital structure | 50.00% |  |  |  |  |  |  |  |
IETL | Ameren Illinois Company | Electric Distribution | Minimum |  |  |  |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Percentage |  |  |  | 50.00% |  |  |  |  |
Pending Rate Case | Ameren Illinois Company |  |  |  |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Electric energy-efficiency rate increase |  |  |  | $ 27 |  |  |  |  |
ICC staff recommended electric energy-efficiency rate increase |  |  |  | $ 24 |  |  |  |  |
Pending Rate Case | Ameren Illinois Company | Electric Distribution |  |  |  |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Public Utilities, Requested Equity Capital Structure, Percentage |  |  |  | 52.00% |  |  |  |  |
ICC staff recommended equity capital structure |  |  |  | 50.00% |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  | $ 117 |  |  |  |  |
ICC staff recommended rate increase |  |  |  | $ 110 |  |  |  |  |
Pending Rate Case | Ameren Illinois Company | Natural gas |  |  |  |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Intervenor recommended return on equity |  |  |  | 9.50% |  |  |  |  |
Intervenor recommended equity capital structure |  |  |  | 52.00% |  |  |  |  |
Pending Rate Case | Ameren Illinois Company | Natural gas | Subsequent Event |  |  |  |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Public Utilities, Requested Return on Equity, Percentage | 10.22% |  |  |  |  |  |  |  |
Public Utilities, Requested Equity Capital Structure, Percentage | 52.00% |  |  |  |  |  |  |  |
Rate Base | $ 2,900 |  |  |  |  |  |  |  |
ICC recommended return on equity percentage | 9.89% |  |  |  |  |  |  |  |
ICC staff recommended equity capital structure | 50.00% |  |  |  |  |  |  |  |
ICC staff recommended rate base | $ 2,900 |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount | 140 |  |  |  |  |  |  |  |
ICC staff recommended rate increase | 127 |  |  |  |  |  |  |  |
Revenues | $ 77 |  |  |  |  |  |  |  |
Intervenor recommended equity capital structure | 50.00% |  |  |  |  |  |  |  |
Natural Gas Capital Investments Challenged as Imprudent | $ 53 |  |  |  |  |  |  |  |
Challenged Recoveries Under the QIP | $ 3 |  |  |  |  |  |  |  |
Pending Rate Case | Ameren Illinois Company | Natural gas | Maximum |  |  |  |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Intervenor recommended rate increase |  |  |  | $ 106 |  |  |  |  |
Pending Rate Case | Ameren Illinois Company | Natural gas | Minimum |  |  |  |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Intervenor recommended rate increase |  |  |  | $ 98 |  |  |  |  |

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