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Rate And Regulatory Matters (Narrative-Illinois) (Details) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2023 USD ($) | Dec. 31, 2027 USD ($) | Dec. 31, 2026 USD ($) | Dec. 31, 2025 USD ($) | Dec. 31, 2024 USD ($) | Dec. 31, 2022 USD ($) numberOfProposedPerformanceMetrics windGenerationFacility | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  | $ 7,957 | $ 6,394 | $ 5,794
Capital expenditures |  |  |  |  |  | 3,351 | 3,479 | 3,233
Ameren Illinois Company |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Annual investment in energy-efficiency programs |  |  |  |  |  | 120 |  |
Revenues |  |  |  |  |  | 3,756 | 2,895 | 2,535
Capital expenditures |  |  |  |  |  | $ 1,601 | $ 1,432 | $ 1,447
Ameren Illinois Company | Minimum |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
ICC required RTO cost benefit study duration |  |  |  |  |  | 5 years |  |
Ameren Illinois Company | Maximum |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
ICC required RTO cost benefit study duration |  |  |  |  |  | 10 years |  |
Electric Distribution | Ameren Illinois Company |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Number of Performance Metrics | numberOfProposedPerformanceMetrics |  |  |  |  |  | 7 |  |
Requested Return on Equity Adjustment |  |  |  |  |  | 0.24% |  |
IETL | Ameren Illinois Company |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Energy Transition Assistance Fund Surcharge |  |  |  |  |  | $ 25 |  |
IETL | Ameren Illinois Company | Maximum |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Energy Transition Assistance Fund Surcharge |  |  |  |  |  | $ 50 |  |
IETL | Electric Distribution | Ameren Illinois Company |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Amortization Period |  |  |  |  |  | 2 years |  |
Amortization Start Date |  |  |  |  |  | 1 year |  |
Multi-Year Rate Plan Reconciliation Cap |  |  |  |  |  | 105.00% |  |
Rate Case Filing Frequency |  |  |  |  |  | 4 years |  |
IETL | Electric Distribution | Ameren Illinois Company | Subsequent Event |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Multi-year rate plan requested revenue requirement |  | $ 1,556 | $ 1,477 | $ 1,373 | $ 1,282 |  |  |
Public Utilities, Requested Return on Equity, Percentage |  | 10.50% | 10.50% | 10.50% | 10.50% |  |  |
Public Utilities, Requested Equity Capital Structure, Percentage |  | 54.03% | 54.02% | 53.97% | 53.99% |  |  |
Rate Base |  | $ 5,300 | $ 5,000 | $ 4,600 | $ 4,300 |  |  |
Public Utilities, Approved Equity Capital Structure, Percentage | 50.00% |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Percentage |  |  |  |  | 50.00% |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  |  | $ 175 |  |  |
IETL | Electric Distribution | Ameren Illinois Company | Minimum |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Percentage |  |  |  |  |  | 50.00% |  |
IETL | Electricity, Generation | Ameren Illinois Company |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Capital expenditures |  |  |  |  |  | $ 20 |  |
Number of Solar Generation Pilot Projects | windGenerationFacility |  |  |  |  |  | 2 |  |
IEIMA revenue requirement reconciliation adjustment | Ameren Illinois Company |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Amortization Period |  |  |  |  |  | 2 years |  |
Final Rate Order | Ameren Illinois Company |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Electric Energy-Efficiency Revenue Requirement |  |  |  |  |  | $ 76 |  |
Renewable energy credits and zero emission credits | Electricity, Generation | Ameren Illinois Company |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  | $ 100 |  |
Pending Rate Case | Natural gas | Ameren Illinois Company | Subsequent Event |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Public Utilities, Requested Return on Equity, Percentage | 10.70% |  |  |  |  |  |  |
Public Utilities, Requested Equity Capital Structure, Percentage | 53.99% |  |  |  |  |  |  |
Rate Base | $ 2,900 |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount | 160 |  |  |  |  |  |  |
Revenues | $ 77 |  |  |  |  |  |  |
IEIMA revenue requirement reconciliation adjustment | Final Rate Order | Electric Distribution | Ameren Illinois Company |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Public Utilities, Approved Equity Capital Structure, Percentage |  |  |  |  |  | 50.00% |  |
Amortization Period |  |  |  |  |  | 2 years |  |
Public Utilities, Approved Rate Increase (Decrease), Amount |  |  |  |  |  | $ 61 |  |
FEJA energy-efficiency rider | Final Rate Order | Ameren Illinois Company |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Public Utilities, Approved Rate Increase (Decrease), Amount |  |  |  |  |  | $ 15 |  |

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