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Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Financial Assets and Liabilities) (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Ameren Missouri |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt Issuance Costs, Net | $ 62 | $ 45
Ameren Illinois |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt Issuance Costs, Net | 51 | 47
Carrying Amount(a) |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt (including current portion) | 17,579 | 15,970
Debt Issuance Costs, Net | 129 | 111
Carrying Amount(a) | Ameren Missouri |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt (including current portion) | 7,745 | 6,341
Debt Issuance Costs, Net | 62 | 45
Carrying Amount(a) | Ameren Illinois |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt (including current portion) | 5,852 | 5,232
Debt Issuance Costs, Net | 51 | 47
Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 15,933 | 14,833
Fair Value | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 15,395 | 14,366
Fair Value | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 538 | 467
Fair Value | Ameren Missouri |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 6,926 | 5,800
Fair Value | Ameren Missouri | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 6,926 | 5,800
Fair Value | Ameren Missouri | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 0 | 0
Fair Value | Ameren Illinois |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 5,243 | 4,867
Fair Value | Ameren Illinois | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 5,243 | 4,867
Fair Value | Ameren Illinois | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | $ 0 | $ 0

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- Definition Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 1A -Publisher FASB -URI https://asc.fasb.org/1943274/2147482925/835-30-45-1A Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482925/835-30-45-2 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482900/835-30-50-1 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1D -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D + Details
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