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Callaway Energy Center (Fair Values Of Investments In Debt And Equity Securities In Nuclear Decommissioning Trust Fund) (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Nuclear Waste Matters [Line Items] |  |  |  |
Debt Securities, Available-for-sale, Amortized Cost | $ 488 |  |  |
Cash and cash equivalents | 420 | $ 328 | $ 272 | $ 216
Fair Value | 1,526 | 1,342 |  |
Cash and cash equivalents | 13 | 7 |  |
Ameren Missouri |  |  |  |
Nuclear Waste Matters [Line Items] |  |  |  |
Debt, Equity, Marketable, And Other Securities, Available-For-Sale, Amortized Cost | 679 | 625 |  |
Cash and cash equivalents | 68 | 17 | $ 10 | $ 13
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax | 865 | 742 |  |
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | 18 | 25 |  |
Fair Value | 1,526 | 1,342 |  |
Cash and cash equivalents | 6 | 0 |  |
Debt, Equity, Marketable, And Other Securities, Available-For-Sale | 1,526 | 1,342 |  |
Ameren Missouri | Debt securities |  |  |  |
Nuclear Waste Matters [Line Items] |  |  |  |
Debt Securities, Available-for-sale, Amortized Cost | 488 | 437 |  |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 7 | 2 |  |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 9 | 17 |  |
Fair Value | 486 | 422 |  |
Ameren Missouri | Equity securities |  |  |  |
Nuclear Waste Matters [Line Items] |  |  |  |
Available-for-sale Equity Securities, Amortized Cost Basis | 179 | 179 |  |
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax | 858 | 740 |  |
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax | 9 | 8 |  |
Equity Securities, FV-NI | 1,028 | 911 |  |
Ameren Missouri | Cash and cash equivalents |  |  |  |
Nuclear Waste Matters [Line Items] |  |  |  |
Marketable Securities | 8 | 10 |  |
Cash and cash equivalents | 0 | 0 |  |
Cash and Cash Equivalents and Restricted Cash and Cash Equivalents | 0 | 0 |  |
Cash and cash equivalents | 8 | 10 |  |
Ameren Missouri | Other Debt And Equity Securities |  |  |  |
Nuclear Waste Matters [Line Items] |  |  |  |
Net Receivables (Payables) From Pending Securities Sales, Interest, and Securities Purchases, Cost Basis | 4 | (1) |  |
Net Receivables (Payables) From Pending Securities Sales, Interest, And Securities Purchases, Available-For-sale Securities, Accumulated Gross Unrealized Gain, Before Tax | 0 | 0 |  |
Net Receivables (Payables) From Pending Securities Sales, Interest, And Securities Purchases, Available-For-sale Securities, Accumulated Gross Unrealized Loss, Before Tax | 0 | 0 |  |
Net Receivables (Payables) From Pending Securities Sales, Interest, and Securities Purchases, Fair Value | $ 4 | $ (1) |  |

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- Definition Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
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- Definition Decommission fund to pay for the costs of decontaminating and decommissioning of facilities through collection of revenues derived from utility assessments and government appropriations. Decommission fund investment for the process whereby a power station, at the end of its economic life, is taken permanently out of service and its site made available for other purposes. In the case of a nuclear station this comprises three different states of clearance. Immediately after the final closure, radioactive material such as nuclear fuel and operational waste is removed and the buildings surrounding the reactor shield are dismantled and finally the reactor itself is dismantled. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(12)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 + Details
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