Related Party Transactions (Narrative) (Details) $ in Millions	12 Months Ended
Dec. 31, 2025 USD ($) MWh $ / MWh	Dec. 31, 2024 USD ($)
Related Party Transaction [Line Items]
Interconnection agreement, optional termination period	3 years
Other assets	$ 1,154	$ 1,123
Ameren Illinois
Related Party Transaction [Line Items]
Other assets	789	697
Ameren Missouri
Related Party Transaction [Line Items]
Other assets	244	254
Ameren Illinois Capacity Supply Agreements with Ameren Missouri \| Ameren Illinois \| 2021 Procurements
Related Party Transaction [Line Items]
Energy supply agreements amount	$ 2
Ameren Services Support Services Agreement
Related Party Transaction [Line Items]
Support services agreement, optional termination period	60 days
Ameren Services Support Services Agreement \| Ameren Illinois
Related Party Transaction [Line Items]
Other assets	$ 38	32
Ameren Services Support Services Agreement \| Ameren Missouri
Related Party Transaction [Line Items]
Other assets	$ 36	$ 29
Ameren Illinois Power Supply Agreements with Ameren Missouri \| Ameren Illinois \| September 2021 Procurement [Member]
Related Party Transaction [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power \| MWh	136,000
Related Party Long Term Contract For Purchase Of Electric Power Rate \| $ / MWh	37

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Related Party Long Term Contract For Purchase Of Electric Power

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Related Party Transaction, Interconnection Agreement, Optional Termination Period

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Related Party Transaction, Support Services Agreement, Optional Termination Period

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- Definition

Amount of noncurrent assets classified as other.

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