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Rate and Regulatory Matters (Narrative-Missouri) (Details) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Feb. 28, 2026 USD ($) | Sep. 30, 2025 MWh | Jun. 30, 2025 MWh | Sep. 30, 2024 MWh | Dec. 31, 2023 MWh | Mar. 31, 2023 MWh | Dec. 31, 2028 USD ($) | Dec. 31, 2027 USD ($) | Dec. 31, 2026 USD ($) | Dec. 31, 2025 USD ($) MWh GW | Dec. 31, 2024 USD ($) | Dec. 31, 2023 USD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Depreciation and amortization |  |  |  |  |  |  |  |  |  | $ 1,568 | $ 1,590 | $ 1,387
Capital expenditures |  |  |  |  |  |  |  |  |  | $ 4,128 | 4,319 | 3,597
Forecast |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Capital expenditures |  |  |  |  |  |  |  |  | $ 1,300 |  |  |
Ameren Missouri |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
PISA deferral percentage |  |  |  |  |  |  |  |  |  | 85.00% |  |
Depreciation and amortization |  |  |  |  |  |  |  |  |  | $ 860 | 917 | 783
Capital expenditures |  |  |  |  |  |  |  |  |  | 2,502 | $ 2,712 | $ 1,760
Ameren Missouri | Solar Generation Facilities |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Capital expenditures |  |  |  |  |  |  |  |  |  | 200 |  |
Ameren Missouri | Natural Gas Generation Facility |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Capital expenditures |  |  |  |  |  |  |  |  |  | 900 |  |
Ameren Missouri | Split Rail Solar Project | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Capital expenditures | $ 600 |  |  |  |  |  |  |  |  |  |  |
Ameren Missouri | Big Hollow Energy Center |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Capital expenditures |  |  |  |  |  |  |  |  |  | $ 2,000 |  |
Ameren Missouri | Electric |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Frequency of Integrated Resource Plan Filings |  |  |  |  |  |  |  |  |  | 4 years |  |
Large load customer rate plan megawatts requested | MWh |  |  |  |  |  |  |  |  |  | 75 |  |
Minimum service term for large load customer rate plan |  |  |  |  |  |  |  |  |  | 12 years |  |
Optional ramp up period for large load customer rate plan |  |  |  |  |  |  |  |  |  | 5 years |  |
Minimum demand charges as percentage of contracted capacity for large load customer rate plan |  |  |  |  |  |  |  |  |  | 80.00% |  |
Maximum ROE under Large Load Customer Rate Plan |  |  |  |  |  |  |  |  |  | 9.74% |  |
Deferral percentage if max ROE exceeded under large load tariff |  |  |  |  |  |  |  |  |  | 65.00% |  |
Gigawatts under contract for large load customer rate plan | GW |  |  |  |  |  |  |  |  |  | 2.2 |  |
Ameren Missouri | Electric | Final Rate Order |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Approved rate increase (decrease), amount |  |  |  |  |  |  |  |  |  | $ 355 |  |
Depreciation and amortization |  |  |  |  |  |  |  |  |  | $ 70 |  |
Ameren Missouri | Natural gas |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of days after end of test year to perform reconciliation when using a future test year |  |  |  |  |  |  |  |  |  | 45 days |  |
Ameren Missouri | Natural gas | Final Rate Order |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Approved rate increase (decrease), amount |  |  |  |  |  |  |  |  |  | $ 32 |  |
Ameren Missouri | Self-build | Natural Gas Generation Facility |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Amount of Megawatts | MWh |  |  | 800 | 800 |  |  |  |  |  |  |  |
Ameren Missouri | Self-build | Solar generation facility |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Amount of Megawatts | MWh |  | 250 |  |  | 50 | 50 |  |  |  |  |  |
Ameren Missouri | Self-build | Energy Storage Facility |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Amount of Megawatts | MWh |  |  | 400 |  |  |  |  |  |  |  |  |
Ameren Missouri | Build-transfer | Solar generation facility |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Amount of Megawatts | MWh |  |  |  |  | 300 |  |  |  |  |  |  |
Ameren Missouri | MEEIA 2025 | Electric | Forecast |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Energy efficiency investments in MEEIA 2025 programs |  |  |  |  |  |  | $ 22 | $ 51 |  |  |  |

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