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Amount of cash inflow for proceeds from settlement of insurance claim, classified as investing activities. Excludes insurance settlement classified as operating activities.

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Callaway Energy Center (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Nuclear Waste Matters [Line Items]
Miscellaneous accounts receivable		$ 85.0	$ 65.0
Accidental Outage - Nuclear Electric Insurance Ltd
Nuclear Waste Matters [Line Items]
Amount of Weekly Indemnity Coverage Commencing Twelve Weeks After Power Outage		4.5
Non-radiation event
Nuclear Waste Matters [Line Items]
Miscellaneous accounts receivable		33.0
Non-radiation event \| Subsequent Event
Nuclear Waste Matters [Line Items]
Proceeds from Insurance Settlement, Investing Activities	$ 17.0
Union Electric Company
Nuclear Waste Matters [Line Items]
Miscellaneous accounts receivable		$ 71.0	$ 36.0
Frequency of Decommissioning Cost Study		3 years
Union Electric Company \| Minimum \| Nuclear Decommissioning Trust Fund
Nuclear Waste Matters [Line Items]
Trust Fund Investments, Target Allocation Percentage		60.00%
Union Electric Company \| Maximum \| Nuclear Decommissioning Trust Fund
Nuclear Waste Matters [Line Items]
Trust Fund Investments, Target Allocation Percentage		70.00%
Union Electric Company \| Nuclear Plant
Nuclear Waste Matters [Line Items]
Estimated Nuclear Generator Repairs		$ 60.0
Annual decommissioning costs included in costs of service		$ 7.0