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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, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | --- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | $ 272 | $ 216 | $ 155 | $ 301
Short-term debt | 536 | 1,070 |  |
Ameren Missouri |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 10 | 13 | 8 | 145
Short-term debt | 170 | 329 |  |
Debt Issuance Costs, Net | 45 | 41 |  |
Ameren Missouri | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term debt | 170 | 329 |  |
Ameren Missouri | Related Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term debt | 306 | 0 |  |
Ameren Illinois |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 234 | 191 | $ 133 | $ 147
Short-term debt | 366 | 264 |  |
Debt Issuance Costs, Net | 47 | 44 |  |
Ameren Illinois | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term debt | 366 | 264 |  |
Ameren Illinois | Related Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term debt | 135 | 0 |  |
Carrying Amount |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 272 | 216 |  |
Long-term debt (including current portion) | 15,970 | 14,025 |  |
Investments in industrial development revenue bonds |  | 240 |  |
Debt Issuance Costs, Net | 111 | 99 |  |
Carrying Amount | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term debt | 536 | 1,070 |  |
Carrying Amount | Ameren Missouri |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 10 | 13 |  |
Long-term debt (including current portion) | 6,341 | 6,086 |  |
Investments in industrial development revenue bonds |  | 240 |  |
Debt Issuance Costs, Net | 45 | 41 |  |
Carrying Amount | Ameren Missouri | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term debt | 170 | 329 |  |
Carrying Amount | Ameren Missouri | Related Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term debt | 306 |  |  |
Carrying Amount | Ameren Illinois |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 234 | 191 |  |
Long-term debt (including current portion) | 5,232 | 4,835 |  |
Debt Issuance Costs, Net | 47 | 44 |  |
Carrying Amount | Ameren Illinois | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term debt | 366 | 264 |  |
Carrying Amount | Ameren Illinois | Related Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term debt | 135 |  |  |
Fair Value |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 272 | 216 |  |
Long-term Debt, Fair Value | 14,833 | 12,453 |  |
Investments, Fair Value Disclosure |  | 240 |  |
Fair Value | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 536 | 1,070 |  |
Fair Value | Level 1 |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 272 | 216 |  |
Long-term Debt, Fair Value | 0 | 0 |  |
Investments, Fair Value Disclosure |  | 0 |  |
Fair Value | Level 1 | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 0 | 0 |  |
Fair Value | Level 2 |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 0 | 0 |  |
Long-term Debt, Fair Value | 14,366 | 11,989 |  |
Investments, Fair Value Disclosure |  | 240 |  |
Fair Value | Level 2 | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 536 | 1,070 |  |
Fair Value | Level 3 |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 0 | 0 |  |
Long-term Debt, Fair Value | 467 | 464 |  |
Investments, Fair Value Disclosure |  | 0 |  |
Fair Value | Level 3 | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 0 | 0 |  |
Fair Value | Ameren Missouri |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 10 | 13 |  |
Long-term Debt, Fair Value | 5,800 | 5,365 |  |
Investments, Fair Value Disclosure |  | 240 |  |
Fair Value | Ameren Missouri | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 170 | 329 |  |
Fair Value | Ameren Missouri | Related Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 306 |  |  |
Fair Value | Ameren Missouri | Level 1 |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 10 | 13 |  |
Long-term Debt, Fair Value | 0 | 0 |  |
Investments, Fair Value Disclosure |  | 0 |  |
Fair Value | Ameren Missouri | Level 1 | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 0 | 0 |  |
Fair Value | Ameren Missouri | Level 1 | Related Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 0 |  |  |
Fair Value | Ameren Missouri | Level 2 |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 0 | 0 |  |
Long-term Debt, Fair Value | 5,800 | 5,365 |  |
Investments, Fair Value Disclosure |  | 240 |  |
Fair Value | Ameren Missouri | Level 2 | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 170 | 329 |  |
Fair Value | Ameren Missouri | Level 2 | Related Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 306 |  |  |
Fair Value | Ameren Missouri | Level 3 |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 0 | 0 |  |
Long-term Debt, Fair Value | 0 | 0 |  |
Investments, Fair Value Disclosure |  | 0 |  |
Fair Value | Ameren Missouri | Level 3 | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 0 | 0 |  |
Fair Value | Ameren Missouri | Level 3 | Related Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 0 |  |  |
Fair Value | Ameren Illinois |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 234 | 191 |  |
Long-term Debt, Fair Value | 4,867 | 4,320 |  |
Fair Value | Ameren Illinois | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 366 | 264 |  |
Fair Value | Ameren Illinois | Related Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 135 |  |  |
Fair Value | Ameren Illinois | Level 1 |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 234 | 191 |  |
Long-term Debt, Fair Value | 0 | 0 |  |
Fair Value | Ameren Illinois | Level 1 | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 0 | 0 |  |
Fair Value | Ameren Illinois | Level 1 | Related Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 0 |  |  |
Fair Value | Ameren Illinois | Level 2 |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 0 | 0 |  |
Long-term Debt, Fair Value | 4,867 | 4,320 |  |
Fair Value | Ameren Illinois | Level 2 | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 366 | 264 |  |
Fair Value | Ameren Illinois | Level 2 | Related Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 135 |  |  |
Fair Value | Ameren Illinois | Level 3 |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 0 | 0 |  |
Long-term Debt, Fair Value | 0 | 0 |  |
Fair Value | Ameren Illinois | Level 3 | Nonrelated Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | 0 | $ 0 |  |
Fair Value | Ameren Illinois | Level 3 | Related Party |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Short-term Debt, Fair Value | $ 0 |  |  |

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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 Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482913/230-10-50-8 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 24 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482740/230-10-45-24 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482740/230-10-45-4 + Details
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- Definition Amount, after allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481830/320-10-45-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(6)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1 + Details
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