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Fair Value Measurements (Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Millions | Dec. 31, 2025 | Dec. 31, 2024
--- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | $ 1,514 | $ 1,333
Excluded receivables, payables, and accrued income, net | 12 | 9
Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 1,028 | 911
Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 486 | 422
Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 0 | 0
Power | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 11 | 6
Commodity Contract |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 16 | 16
Nuclear Decommissioning Trust Fund | 1,514 | 1,333
Assets | 1,530 | 1,349
Derivative liabilities | 126 | 103
Commodity Contract | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 0 | 0
Nuclear Decommissioning Trust Fund | 1,028 | 911
Assets | 1,028 | 911
Derivative liabilities | 6 | 5
Commodity Contract | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 3 | 7
Nuclear Decommissioning Trust Fund | 486 | 422
Assets | 489 | 429
Derivative liabilities | 51 | 39
Commodity Contract | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 13 | 9
Nuclear Decommissioning Trust Fund | 0 | 0
Assets | 13 | 9
Derivative liabilities | 69 | 59
Ameren Missouri |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets | 1,526 | 1,343
Ameren Missouri | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets | 1,028 | 911
Ameren Missouri | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets | 487 | 426
Ameren Missouri | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets | 11 | 6
Ameren Missouri | Fuel oils |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liabilities | 5 | 4
Ameren Missouri | Fuel oils | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liabilities | 5 | 4
Ameren Missouri | Fuel oils | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liabilities | 0 | 0
Ameren Missouri | Fuel oils | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liabilities | 0 | 0
Ameren Missouri | Natural gas |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 1 | 4
Derivative liabilities | 10 | 11
Ameren Missouri | Natural gas | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 0 | 0
Derivative liabilities | 0 | 0
Ameren Missouri | Natural gas | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 1 | 4
Derivative liabilities | 10 | 11
Ameren Missouri | Natural gas | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 0 | 0
Derivative liabilities | 0 | 0
Ameren Missouri | Power |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 11 | 6
Ameren Missouri | Power | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 0 | 0
Ameren Missouri | Power | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 0 | 0
Ameren Missouri | Power | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 11 | 6
Ameren Missouri | Commodity Contract |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 12 | 10
Derivative liabilities | 15 | 15
Ameren Missouri | Commodity Contract | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 0 | 0
Derivative liabilities | 5 | 4
Ameren Missouri | Commodity Contract | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 1 | 4
Derivative liabilities | 10 | 11
Ameren Missouri | Commodity Contract | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 11 | 6
Derivative liabilities | 0 | 0
Ameren Missouri | Equity securities | U.S. large capitalization |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 1,028 | 911
Ameren Missouri | Equity securities | U.S. large capitalization | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 1,028 | 911
Ameren Missouri | Equity securities | U.S. large capitalization | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 0 | 0
Ameren Missouri | Equity securities | U.S. large capitalization | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 0 | 0
Ameren Missouri | Debt securities | U.S. Treasury and agency securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 225 | 191
Ameren Missouri | Debt securities | U.S. Treasury and agency securities | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 0 | 0
Ameren Missouri | Debt securities | U.S. Treasury and agency securities | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 225 | 191
Ameren Missouri | Debt securities | U.S. Treasury and agency securities | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 0 | 0
Ameren Missouri | Debt securities | Corporate bonds |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 177 | 145
Ameren Missouri | Debt securities | Corporate bonds | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 0 | 0
Ameren Missouri | Debt securities | Corporate bonds | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 177 | 145
Ameren Missouri | Debt securities | Corporate bonds | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 0 | 0
Ameren Missouri | Debt securities | Diversified credit |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 84 | 86
Ameren Missouri | Debt securities | Diversified credit | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 0 | 0
Ameren Missouri | Debt securities | Diversified credit | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 84 | 86
Ameren Missouri | Debt securities | Diversified credit | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Nuclear Decommissioning Trust Fund | 0 | 0
Ameren Illinois | Natural gas |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 4 | 6
Derivative liabilities | 32 | 35
Ameren Illinois | Natural gas | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 0 | 0
Derivative liabilities | 1 | 1
Ameren Illinois | Natural gas | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 2 | 3
Derivative liabilities | 28 | 28
Ameren Illinois | Natural gas | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 2 | 3
Derivative liabilities | 3 | 6
Ameren Illinois | Power |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liabilities | 79 | 53
Ameren Illinois | Power | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liabilities | 0 | 0
Ameren Illinois | Power | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liabilities | 13 | 0
Ameren Illinois | Power | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liabilities | 66 | 53
Ameren Illinois | Commodity Contract |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 4 | 6
Derivative liabilities | 111 | 88
Ameren Illinois | Commodity Contract | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 0 | 0
Derivative liabilities | 1 | 1
Ameren Illinois | Commodity Contract | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 2 | 3
Derivative liabilities | 41 | 28
Ameren Illinois | Commodity Contract | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative assets | 2 | 3
Derivative liabilities | $ 69 | $ 59

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- Definition Fair value portion of asset recognized for present right to economic benefit. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 100 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-100 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
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- Definition The fair value of investments held in a trust fund to pay for the costs of decontaminating and decommissioning facilities, whether such amount is presented as a separate caption or as a parenthetical disclosure on the balance sheet. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481850/410-20-50-1 + Details
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