Callaway Energy Center (Insurance Disclosure) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Apr. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Nuclear Waste Matters [Line Items]
Decommissioning Cost		$ 7.0
Frequency of Decommissioning Cost Study		3 years
Miscellaneous accounts receivable		$ 87.0	$ 85.0
Number Of Years The Limit Of Liability And The Maximum Potential Annual Payments Are Adjusted		5 years
Number Of Weeks Of Coverage After The First Twelve Weeks Of An Outage		1
Number Of Additional Weeks After Initial Indemnity Coverage For Power Outage		1.365
Subsequent Event
Nuclear Waste Matters [Line Items]
Proceeds from Insurance Settlement, Investing Activities	$ 22.0
Union Electric Company
Nuclear Waste Matters [Line Items]
Miscellaneous accounts receivable		$ 57.0	$ 71.0
Public Liability And Nuclear Worker Liability - American Nuclear Insurers
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage		450.0
Insurance Maximum Coverage per Incident		0.0
Public Liability And Nuclear Worker Liability - Pool Participation
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage		13,073.0
Insurance Maximum Coverage per Incident		138.0
Threshold Amount For Retrospective Insurance Assessment For Covered Loss Under Public Liability And Nuclear Worker Liability Insurance Policy		450.0
Maximum Annual Payment Per Incident At Licensed Commercial Nuclear Reactor		21.0
Public Liability
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage		13,523.0
Insurance Maximum Coverage per Incident		138.0
Property Damage - Nuclear Electric Insurance Ltd
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage		3,200.0
Insurance Maximum Coverage per Incident		26.0
Accidental Outage - Nuclear Electric Insurance Ltd
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage		490.0
Insurance Maximum Coverage per Incident		7.0
Amount Of Weekly Indemnity Coverage Commencing Twelve Weeks After Power Outage		4.5
Amount Of Additional Weekly Indemnity Coverage Commencing After Initial Indemnity Coverage		3.6
Amount Of Weekly Indemnity Coverage Thereafter Not Exceeding Policy Limit		490.0
Sub-Limit Of Amount Of Weekly Indemnity Coverage Thereafter Not Exceeding Policy Limit For Non-Nuclear Events		328.0
Radiation Event
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage		2,700.0
Aggregate Nuclear Power Industry Insurance Policy Limit For Losses From Terrorist Attacks Within Twelve Month Period		3,200.0
Non-Radiation Event
Nuclear Waste Matters [Line Items]
Miscellaneous accounts receivable		26.0
Insurance Aggregate Maximum Coverage		2,300.0
Aggregate Nuclear Power Industry Insurance Policy Limit For Losses From Terrorist Attacks Within Twelve Month Period		1,800.0
Property Damage European Mutual Association for Nuclear Insurance
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage		$ 490.0