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Derivative Financial Instruments (Open Gross Derivative Volumes By Commodity Type) (Detail) lb in Thousands, gal in Millions, MWh in Millions, MMBTU in Millions | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2023 MWh MMBTU lb gal | Dec. 31, 2022 MMBTU MWh lb gal
Fuel oils |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Volume | gal | 18 | 18
Natural gas |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 275 | 205
Power |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 6 | 7
Uranium |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Mass | lb | 186 | 514
Union Electric Company | Fuel oils |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Volume | gal | 18 | 18
Union Electric Company | Natural gas |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 57 | 48
Union Electric Company | Power |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 1 | 1
Union Electric Company | Uranium |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Mass | lb | 186 | 514
Ameren Illinois Company | Fuel oils |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Volume | gal | 0 | 0
Ameren Illinois Company | Natural gas |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 218 | 157
Ameren Illinois Company | Power |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 5 | 6
Ameren Illinois Company | Uranium |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Mass | lb | 0 | 0

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 815 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480237/815-40-50-5 + Details
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- Definition Nominal energy measure used to calculate payments on a derivative instrument. + References No definition available. + Details
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- Definition Nominal mass used to calculate payments on a derivative instrument. + References No definition available. + Details
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- Definition Nominal volume used to calculate payments on a derivative instrument. + References No definition available. + Details
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