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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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