Related Party Transactions Narrative (Details) - April 2017 Procurement [Member] - Ameren Illinois Company - Ameren Illinois Power Supply Agreements with Ameren Missouri	3 Months Ended
Mar. 31, 2017 MWh $ / MWh
Related Party Transaction [Line Items]
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power \| MWh	85,600
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power, Rate \| $ / MWh	33.64

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.

No definition available.

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