Callaway Energy Center (Narrative) (Details) - Union Electric Company $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Nuclear Waste Matters [Line Items]
Frequency of Decommissioning Cost Study	3 years
Nuclear Plant
Nuclear Waste Matters [Line Items]
Estimated Nuclear Generator Repairs	$ 65
Annual decommissioning costs included in costs of service	$ 7
Minimum | Nuclear Decommissioning Trust Fund
Nuclear Waste Matters [Line Items]
Trust Fund Investments, Target Allocation Percentage	60.00%
Maximum | Nuclear Decommissioning Trust Fund
Nuclear Waste Matters [Line Items]
Trust Fund Investments, Target Allocation Percentage	70.00%