Related Party Transactions (Schedule of Related Party Electric Power Supply Agreements) (Details) - Ameren Illinois Company - Ameren Illinois Power Supply Agreements with Ameren Missouri	12 Months Ended
	Dec. 31, 2019 MWh $ / MWh
September 2015 Procurement
Schedule of Related Party Electric Power Supply Agreements [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power | MWh	339,000
Related Party Long Term Contract For Purchase Of Electric Power Rate | $ / MWh	38
April 2016 Procurement
Schedule of Related Party Electric Power Supply Agreements [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power | MWh	375,200
Related Party Long Term Contract For Purchase Of Electric Power Rate | $ / MWh	35
September 2016 Procurement
Schedule of Related Party Electric Power Supply Agreements [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power | MWh	82,800
Related Party Long Term Contract For Purchase Of Electric Power Rate | $ / MWh	34
April 2017 Procurement
Schedule of Related Party Electric Power Supply Agreements [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power | MWh	85,600
Related Party Long Term Contract For Purchase Of Electric Power Rate | $ / MWh	34
April 2018 Procurement
Schedule of Related Party Electric Power Supply Agreements [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power | MWh	110,000
Related Party Long Term Contract For Purchase Of Electric Power Rate | $ / MWh	32
April 2019 Procurement
Schedule of Related Party Electric Power Supply Agreements [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power | MWh	288,000
Related Party Long Term Contract For Purchase Of Electric Power Rate | $ / MWh	35
September 2019 Procurement
Schedule of Related Party Electric Power Supply Agreements [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power | MWh	170,800
Related Party Long Term Contract For Purchase Of Electric Power Rate | $ / MWh	29