Related Party Transactions (Narrative) (Details) - Ameren Illinois Company - April 2021 Procurement - Ameren Illinois Power Supply Agreements with Ameren Missouri	3 Months Ended
Mar. 31, 2021 MWh $ / MWh
Related Party Transaction [Line Items]
Related Party Long Term Contract For Purchase of Electric Power \| MWh	33,600
Related Party Long Term Contract For Purchase of Electric Power Rate \| $ / MWh	34

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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