Related Party Transactions Narrative (Details) - April 2018 Procurement [Member] - Ameren Illinois Company - Ameren Illinois Power Supply Agreements with Ameren Missouri |
3 Months Ended | 6 Months Ended |
|---|---|---|
|
Jun. 30, 2018
$ / MWh
|
Jun. 30, 2018
MWh
|
|
| Related Party Transaction [Line Items] | ||
| Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power | MWh | 110,000 | |
| Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power, Rate | $ / MWh | 32 |