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Long-Term Debt And Equity Financings (Narrative) (Details) - USD ($) |  | 1 Months Ended | 12 Months Ended |  |  |  |  |  |  |  |  |
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Feb. 11, 2021 | Jan. 31, 2023 | Nov. 30, 2022 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Jan. 31, 2024 | Jun. 30, 2023 | May 31, 2023 | Mar. 31, 2023 | Sep. 30, 2022 | Aug. 31, 2022 | May 31, 2022 | Apr. 30, 2022 | May 31, 2021
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, authorized (in shares) |  |  |  | 100,000,000 |  |  |  |  |  |  |  |  |  |  |
Preferred stock, par value (in dollars per share) |  |  |  | $ 0.01 |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares outstanding (in shares) |  |  |  | 0 |  |  |  |  |  |  |  |  |  |  |
Shares issued under the DRPlus and 401(k) plan |  |  |  | 600,000 | 500,000 | 500,000 |  |  |  |  |  |  |  |  |
Issuances of common stock |  |  |  | $ 346,000,000 | $ 333,000,000 | $ 308,000,000 |  |  |  |  |  |  |  |  |
Accrued Proceeds from Issuance of Common Stock |  |  |  | $ 7,000,000 | $ 8,000,000 |  |  |  |  |  |  |  |  |  |
Shares issued (in shares) |  |  |  | 500,000 | 400,000 | 500,000 |  |  |  |  |  |  |  |  |
Value of stock issued |  |  |  |  | $ 31,000,000 |  |  |  |  |  |  |  |  |  |
Common stock, shares authorized under DRPlus plan (in shares) |  |  |  |  |  |  |  |  | 3,000,000 |  |  |  |  |  |
Common stock, shares authorized under 401(k) Plan (in shares) |  |  |  |  |  |  |  |  |  |  |  |  | 7,500,000 |  |
Maximum value of shares to be issued under ATM Program |  |  |  | $ 770,000,000 |  |  |  |  |  |  |  |  |  |  | $ 1,750,000,000
Number of shares issued under ATM Program (in shares) |  |  |  | 3,200,000 | 3,400,000 | 1,800,000 |  |  |  |  |  |  |  |  |
Value of shares issued under ATM program |  |  |  | $ 299,000,000 | $ 292,000,000 | $ 148,000,000 |  |  |  |  |  |  |  |  |
Payments of stock issuance costs |  |  |  | $ 3,000,000 | $ 3,000,000 | $ 2,000,000 |  |  |  |  |  |  |  |  |
Initial forward sale price, basis spread |  |  |  | 0.0075 |  |  |  |  |  |  |  |  |  |  |
Shares issued under non-ATM program forward sale agreement | 1,600,000 |  |  | 0 | 0 | 1,600,000 |  |  |  |  |  |  |  |  |
Cash settlement of forward sale agreement | $ 113,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Termination of a financing obligation |  |  |  | $ 240,000,000 | $ 0 | $ 0 |  |  |  |  |  |  |  |  |
Debt default provision excess |  |  |  | 25,000,000 |  |  |  |  |  |  |  |  |  |  |
Principal payment |  |  |  | $ 849,000,000 |  |  |  |  |  |  |  |  |  |  |
Forward Sale Agreements Outstanding |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares to settle forward sale agreements (in shares) |  |  |  | 2,900,000 |  |  |  |  |  |  |  |  |  |  |
Cash settlement of forward sale agreements |  |  |  | $ 230,000,000 |  |  |  |  |  |  |  |  |  |  |
Period End Net Cash Settlement Price |  |  |  | 24,000,000 |  |  |  |  |  |  |  |  |  |  |
Period end net share settlement price |  |  |  | 300,000 |  |  |  |  |  |  |  |  |  |  |
Forward sale agreement equity offering shares (in shares) |  |  |  | 2,900,000 |  |  |  |  |  |  |  |  |  |  |
Forward Sale Agreement Gross Sales Price |  |  |  | 232,000,000 |  |  |  |  |  |  |  |  |  |  |
Dividend reinvestment and 401 (k) plans |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuances of common stock |  |  |  | 39,000,000 | 41,000,000 | 47,000,000 |  |  |  |  |  |  |  |  |
Ameren (parent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Principal payment |  |  |  | $ 450,000,000 |  |  |  |  |  |  |  |  |  |  |
Ameren Missouri |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, authorized (in shares) |  |  |  | 7,500,000 |  |  |  |  |  |  |  |  |  |  |
Preferred stock, par value (in dollars per share) |  |  |  | $ 1 |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares outstanding (in shares) |  |  |  | 0 |  |  |  |  |  |  |  |  |  |  |
Termination of a financing obligation |  | $ 240,000,000 |  | $ 240,000,000 | 0 | 0 |  |  |  |  |  |  |  |  |
Principal payment |  |  |  | $ 350,000,000 |  |  |  |  |  |  |  |  |  |  |
Ameren Illinois |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, authorized (in shares) |  |  |  | 2,600,000 |  |  |  |  |  |  |  |  |  |  |
Preferred stock, par value (in dollars per share) |  |  |  | $ 0 |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares outstanding (in shares) |  |  |  | 0 |  |  |  |  |  |  |  |  |  |  |
Termination of a financing obligation |  |  |  | $ 0 | 0 | $ 0 |  |  |  |  |  |  |  |  |
Common stock equity to capitalization ratio |  |  |  | 53.00% |  |  |  |  |  |  |  |  |  |  |
Principal payment |  |  |  | $ 0 |  |  |  |  |  |  |  |  |  |  |
Ameren Missouri and Ameren Illinois |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Bonds interest rate assumption |  |  |  | 7.00% |  |  |  |  |  |  |  |  |  |  |
Dividend rate on preferred shares, percentage |  |  |  | 8.00% |  |  |  |  |  |  |  |  |  |  |
Ameren Transmission Company of Illinois |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Principal payment |  |  |  | $ 49,000,000 |  |  |  |  |  |  |  |  |  |  |
First Mortgage Bonds, 3.90%, Due 2052 - $525 Issuance | Ameren Missouri | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  |  |  | $ 525,000,000 | $ 525,000,000 |  |  |  |  |  |  |  |  | $ 525,000,000 |
Long-term debt interest rate |  |  |  | 3.90% |  |  |  |  |  |  |  |  |  | 3.90% |
1992 Series due 2022 | Ameren Missouri | Environmental Improvement And Pollution Control Revenue Bonds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  |  |  |  | 1.60% |  |  |  |  |  |  |  |  |  |
Maturities of Senior Debt |  |  | $ 47,000,000 |  |  |  |  |  |  |  |  |  |  |  |
City Of Bowling Green Agreement - Peno Creek Ct | Ameren Missouri |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturities of Senior Debt |  |  |  |  | $ 8,000,000 |  |  |  |  |  |  |  |  |  |
3.85% First mortgage bonds due 2032 | Ameren Illinois | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  |  |  | $ 500,000,000 | $ 500,000,000 |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  |  |  | 0.0385% |  |  |  |  |  |  |  |  |  |  |
3.85% First mortgage bonds due 2032 | Ameren Illinois | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  |  |  |  | 3.85% |  |  |  |  |  |  |  |  |  |
Senior Secured Notes, 2.70%, Due 2022 | Ameren Illinois | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  |  |  |  |  |  |  |  |  |  | $ 400,000,000 |  |  |  |
Senior Secured Notes, 2.70%, Due 2022 | Ameren Illinois | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  |  |  |  |  |  |  |  |  |  | 0.027% |  |  |  |
5.90% First mortgage bonds due 2052 | Ameren Illinois | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  |  | $ 350,000,000 | $ 350,000,000 | $ 350,000,000 |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  |  | 5.90% | 5.90% |  |  |  |  |  |  |  |  |  |  |
0.375% First Mortgage bonds due 2023 | Ameren Illinois | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  |  |  | $ 0 | 100,000,000 |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  |  |  | 0.375% |  |  |  |  |  |  |  |  |  |  |
0.375% First Mortgage bonds due 2023 | Ameren Illinois | Debt securities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  |  |  |  |  |  |  | $ 100,000,000 |  |  |  |  |  |  |
Long-term debt interest rate |  |  |  |  |  |  |  |  | 0.375% |  |  |  |  |  |
2.96% Senior unsecured notes due 2052 | Ameren Transmission Company of Illinois | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  |  |  | $ 95,000,000 | 95,000,000 |  |  |  |  |  |  | $ 95,000,000 |  |  |
Long-term debt interest rate |  |  |  | 2.96% |  |  |  |  |  |  |  | 2.96% |  |  |
3.43% Senior unsecured notes due 2050 | Ameren Transmission Company of Illinois | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  |  |  | $ 400,000,000 | 400,000,000 |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  |  |  |  |  |  |  |  |  |  |  | 3.43% |  |  |
Ratio of Indebtedness to Net Capital |  |  |  | 0.70 |  |  |  |  |  |  |  |  |  |  |
Ratio of Indebtedness to Total Assets |  |  |  | 0.10 |  |  |  |  |  |  |  |  |  |  |
Principal payment |  |  |  |  |  |  |  |  |  |  |  | $ 50,000,000 |  |  |
5.00% Senior unsecured notes due 2029 | Ameren (parent) | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  |  |  | $ 700,000,000 |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  |  |  | 5.00% |  |  |  |  |  |  |  |  |  |  |
5.45% First mortgage bonds due 2053 | Ameren Missouri | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  |  |  | $ 500,000,000 | 0 |  |  |  |  | $ 500,000,000 |  |  |  |  |
Long-term debt interest rate |  |  |  | 5.45% |  |  |  |  |  | 5.45% |  |  |  |  |
4.95% First mortgage bonds due 2033 | Ameren Illinois | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  |  |  | $ 500,000,000 | $ 0 |  |  |  | $ 500,000,000 |  |  |  |  |  |
Long-term debt interest rate |  |  |  | 0.0495% |  |  |  |  |  |  |  |  |  |  |
4.95% First mortgage bonds due 2033 | Ameren Illinois | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  |  |  |  |  |  |  |  | 4.95% |  |  |  |  |  |
Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward contract indexed to issuer's equity, forward rate per share (in dollars per share) |  |  |  | $ 76.69 |  |  |  |  |  |  |  |  |  |  |
Minimum | Ameren Illinois |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock equity to capitalization ratio |  |  |  | 30.00% |  |  |  |  |  |  |  |  |  |  |
Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward contract indexed to issuer's equity, forward rate per share (in dollars per share) |  |  |  | $ 89.31 |  |  |  |  |  |  |  |  |  |  |
Weighted Average |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward contract indexed to issuer's equity, forward rate per share (in dollars per share) |  |  |  | $ 80.45 |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | First Mortgage Bonds, 5.25%, Due 2054 - $350 Issuance | Ameren Missouri | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  |  |  |  |  |  | $ 350,000,000 |  |  |  |  |  |  |  |
Long-term debt interest rate |  |  |  |  |  |  | 5.25% |  |  |  |  |  |  |  |

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- Definition Additional Shares of Ameren common stock to be issued under its 401(k) plan pursuant to filing a Form S-8 registration statement with the SEC. + References No definition available. + Details
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- Definition Additional Shares of Ameren common stock to be issued under its DRPlus plan pursuant to filing a Form S-3 registration statement with the SEC. + References No definition available. + Details
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