Related Party Transactions (Narrative) (Details) $ in Millions	3 Months Ended
Mar. 31, 2020 USD ($)
Ameren Illinois Company \| April 2020 Procurement \| Ameren Illinois Capacity Supply Agreements with Ameren Missouri
Related Party Transaction [Line Items]
Energy Supply Agreements Amount	$ 2

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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