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Long-Term Debt And Equity Financings (Narrative) (Details) - USD ($) | 1 Months Ended | 4 Months Ended | 12 Months Ended |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jan. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Jan. 05, 2023 | Nov. 10, 2022 | Sep. 30, 2022 | May 31, 2021 | Feb. 11, 2021 | Dec. 29, 2020 | Aug. 05, 2019
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, authorized (in shares) |  | 100,000,000 | 100,000,000 |  |  |  |  |  |  |  |  |
Preferred stock, par value (in dollars per share) |  | $ 0.01 | $ 0.01 |  |  |  |  |  |  |  |  |
Preferred stock, shares outstanding (in shares) |  | 0 | 0 |  |  |  |  |  |  |  |  |
Shares issued under the DRPlus and 401(k) plan |  |  | 500,000 | 500,000 | 700,000 |  |  |  |  |  |  |
Issuances of common stock |  |  | $ 333,000,000 | $ 308,000,000 | $ 476,000,000 |  |  |  |  |  |  |
Stock Issued During Period, Shares, Other |  |  | 400,000 | 500,000 | 500,000 |  |  |  |  |  |  |
Stock Issued |  |  |  | $ 33,000,000 |  |  |  |  |  |  |  |
Common Stock, Shares Authorized Under DRPlus Plan |  | 4,000,000 | 4,000,000 |  |  |  |  |  |  |  |  |
Common Stock, Shares Authorized Under 401(k) Plan |  | 4,000,000 | 4,000,000 |  |  |  |  |  |  |  |  |
Maximum Value Of Shares To Be Issued Under ATM Program |  | $ 1,000,000,000 | $ 1,000,000,000 |  |  |  |  |  | $ 750,000,000 |  |  |
Quantity Of Shares Issued Under ATM Program |  |  | 3,400,000 | 1,800,000 |  |  |  |  |  |  |  |
Value of shares issued under ATM program |  |  | $ 292,000,000 | $ 148,000,000 |  |  |  |  |  |  |  |
Payments of Stock Issuance Costs |  |  | $ 3,000,000 | $ 2,000,000 |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Indexed Shares |  |  |  |  |  |  |  |  |  |  |  | 7,500,000
Initial forward sale price, basis spread |  | 0.0075 | 0.0075 |  |  |  |  |  |  |  |  |
Shares issued under forward sale agreement |  |  | 0 | 1,600,000 | 5,900,000 |  |  |  |  |  |  |
Common Stock Value Issued Through Forward Sale Agreement |  |  |  |  |  |  |  |  |  | $ 113,000,000 | $ 425,000,000 |
Year One |  | $ 340,000,000 | $ 340,000,000 |  |  |  |  |  |  |  |  |
Debt Default Provision Excess |  |  | 25,000,000 |  |  |  |  |  |  |  |  |
Increased Maximum Value of Shares To Be Issued Under ATM Program |  |  |  |  |  |  | $ 1,000,000,000 |  |  |  |  |
Accrued Proceeds from Issuance of Common Stock |  | $ 8,000,000 | $ 8,000,000 |  |  |  |  |  |  |  |  |
Forward Sale Agreements Outstanding |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Shares, at Fair Value |  | 3,200,000 | 3,200,000 |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value |  | $ 295,000,000 | $ 295,000,000 |  |  |  |  |  |  |  |  |
Period End Net Cash Settlement Price |  | 11,000,000 | 11,000,000 |  |  |  |  |  |  |  |  |
Period End Net Share Settlement Price |  | 100,000 | 100,000 |  |  |  |  |  |  |  |  |
Forward Sale Agreement Equity Offering Shares |  | 3,200,000 | 3,200,000 |  |  |  |  |  |  |  |  |
Forward Sale Agreement Gross Sales Price |  | 300,000,000 | 300,000,000 |  |  |  |  |  |  |  |  |
Forward Sale Agreement, Compensation Received by Counterparty |  | $ 3,000,000 | 3,000,000 |  |  |  |  |  |  |  |  |
Dividend reinvestment and 401 (k) plans [Member] |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Issuances of common stock |  |  | $ 41,000,000 | $ 47,000,000 | $ 51,000,000 |  |  |  |  |  |  |
Union Electric Company |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, authorized (in shares) |  | 7,500,000 | 7,500,000 |  |  |  |  |  |  |  |  |
Preferred stock, par value (in dollars per share) |  | $ 1 | $ 1 |  |  |  |  |  |  |  |  |
Preferred stock, shares outstanding (in shares) |  | 0 | 0 |  |  |  |  |  |  |  |  |
Year One |  | $ 240,000,000 | $ 240,000,000 |  |  |  |  |  |  |  |  |
Ameren Illinois Company |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, authorized (in shares) |  | 2,600,000 | 2,600,000 |  |  |  |  |  |  |  |  |
Preferred stock, par value (in dollars per share) |  | $ 0 | $ 0 |  |  |  |  |  |  |  |  |
Preferred stock, shares outstanding (in shares) |  | 0 | 0 |  |  |  |  |  |  |  |  |
Year One |  | $ 100,000,000 | $ 100,000,000 |  |  |  |  |  |  |  |  |
Payments for Repurchase of Redeemable Preferred Stock |  |  | $ 0 | 13,000,000 | $ 0 |  |  |  |  |  |  |
Common stock equity to capitalization ratio |  | 54.00% | 54.00% |  |  |  |  |  |  |  |  |
Ameren Illinois Company | 6.625% Series |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Dividend rate on preferred shares, percentage |  |  | 6.625% |  |  |  |  |  |  |  |  |
Dividends, Preferred Stock, Cash |  |  | $ 12,000,000 |  |  |  |  |  |  |  |  |
Ameren Illinois Company | 7.75% Series |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Dividend rate on preferred shares, percentage |  |  | 7.75% |  |  |  |  |  |  |  |  |
Dividends, Preferred Stock, Cash |  |  | $ 1,000,000 |  |  |  |  |  |  |  |  |
Ameren Missouri and Ameren Illinois |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Bonds interest rate assumption |  | 6.00% | 6.00% |  |  |  |  |  |  |  |  |
Dividend rate on preferred shares, percentage |  |  | 7.00% |  |  |  |  |  |  |  |  |
Ameren Transmission Company of Illinois |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Year One |  | $ 0 | $ 0 |  |  |  |  |  |  |  |  |
Ameren (parent) |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Year One |  | 0 | 0 |  |  |  |  |  |  |  |  |
Senior Secured Notes 1.75% Due 2028 | Ameren (parent) | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  | $ 450,000,000 | $ 450,000,000 | 450,000,000 |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 1.75% | 1.75% |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Unsecured Debt |  |  | $ 447,000,000 |  |  |  |  |  |  |  |  |
Senior Unsecured Notes 1.95% due 2027 | Ameren (parent) | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  | $ 500,000,000 | $ 500,000,000 | 500,000,000 |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 1.95% | 1.95% |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Unsecured Debt |  |  | $ 497,000,000 |  |  |  |  |  |  |  |  |
First Mortgage Bonds, 3.90%, Due 2052 - $525 Issuance | Union Electric Company | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 3.90% | 3.90% |  |  |  |  |  |  |  |  |
First Mortgage Bonds, 3.90%, Due 2052 - $525 Issuance | Union Electric Company | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  | $ 525,000,000 | $ 525,000,000 | 0 |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 3.90% | 3.90% |  |  |  |  |  |  |  |  |
Proceeds from issuance of secured debt |  |  | $ 519,000,000 |  |  |  |  |  |  |  |  |
Senior Secured Notes 2.15% Due 2032 [Member] | Union Electric Company | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 2.15% | 2.15% |  |  |  |  |  |  |  |  |
Senior Secured Notes 2.15% Due 2032 [Member] | Union Electric Company | 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 |  | 2.15% | 2.15% |  |  |  |  |  |  |  |  |
Proceeds from issuance of secured debt |  |  | $ 521,000,000 |  |  |  |  |  |  |  |  |
1992 Series due 2022 | Union Electric Company | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 1.60% | 1.60% |  |  |  |  |  |  |  |  |
1992 Series due 2022 | Union Electric Company | Environmental Improvement And Pollution Control Revenue Bonds |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  | $ 0 | $ 0 | 47,000,000 |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 1.60% | 1.60% |  |  |  |  |  |  |  |  |
Maturities of Senior Debt |  |  | $ 47,000,000 |  |  |  |  |  |  |  |  |
City Of Bowling Green Agreement - Peno Creek Ct | Union Electric Company |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  | $ 0 | 0 | 8,000,000 |  |  |  |  |  |  |  |
Maturities of Senior Debt |  |  | 8,000,000 |  |  |  |  |  |  |  |  |
Audrain County Agreement - Audrain County Ct | Union Electric Company |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  | $ 240,000,000 | $ 240,000,000 | 240,000,000 |  |  |  |  |  |  |  |
First Mortgage Bonds, 3.85%, Due 2032 - $500 Issuance | Ameren Illinois Company | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 0.0385% | 0.0385% |  |  |  |  |  |  |  |  |
First Mortgage Bonds, 3.85%, Due 2032 - $500 Issuance | Ameren Illinois Company | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  | $ 500,000,000 | $ 500,000,000 | 0 |  |  |  |  |  |  |  |
Proceeds from issuance of secured debt |  |  | 496,000,000 |  |  |  |  |  |  |  |  |
Senior Secured Notes, 2.70%, Due 2022 | Ameren Illinois Company | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  | $ 0 | $ 0 | 400,000,000 |  |  |  | $ 400,000,000 |  |  |  |
Long-term debt interest rate |  | 0.027% | 0.027% |  |  |  |  |  |  |  |  |
First Mortgage Bonds, 5.90%, $350 Million Due 2052 | Ameren Illinois Company | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 5.90% | 5.90% |  |  |  |  |  |  |  |  |
First Mortgage Bonds, 5.90%, $350 Million Due 2052 | Ameren Illinois Company | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  | $ 350,000,000 | $ 350,000,000 | 0 |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 5.90% | 5.90% |  |  |  |  |  |  |  |  |
Proceeds from issuance of secured debt |  |  | $ 346,000,000 |  |  |  |  |  |  |  |  |
First Mortgage Bonds, 2.90%, $350 Million Due 2051 | Union Electric Company | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 2.90% | 2.90% |  |  |  |  |  |  |  |  |
First Mortgage Bonds, 2.90%, $350 Million Due 2051 | Ameren Illinois Company | 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 |  | 2.90% | 2.90% |  |  |  |  |  |  |  |  |
Proceeds from issuance of secured debt |  |  | $ 345,000,000 |  |  |  |  |  |  |  |  |
First Mortgage Bonds, 0.375%, $100 Million Due 2023 | Union Electric Company | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 0.375% | 0.375% |  |  |  |  |  |  |  |  |
First Mortgage Bonds, 0.375%, $100 Million Due 2023 | Ameren Illinois Company | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  | $ 100,000,000 | $ 100,000,000 | 100,000,000 |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 0.375% | 0.375% |  |  |  |  |  |  |  |  |
Proceeds from issuance of secured debt |  |  | $ 100,000,000 |  |  |  |  |  |  |  |  |
Senior Unsecured Notes, 2.96%, 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 | 0 |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 2.96% | 2.96% |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Unsecured Debt |  | $ 95,000,000 |  |  |  |  |  |  |  |  |  |
Senior Unsecured Notes, 2.96%, Due 2052 | Ameren Transmission Company of Illinois | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 2.96% | 2.96% |  |  |  |  |  |  |  |  |
Senior Unsecured Notes, 3.43%, 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 | 450,000,000 |  |  |  |  |  |  |  |
Year One |  | $ 50,000,000 | $ 50,000,000 |  |  |  |  |  |  |  |  |
Ratio of Indebtedness to Net Capital |  | 0.70 | 0.70 |  |  |  |  |  |  |  |  |
Ratio of Indebtedness to Total Assets |  | 0.10 | 0.10 |  |  |  |  |  |  |  |  |
Senior Unsecured Notes, 3.43%, Due 2050 | Ameren Transmission Company of Illinois | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 3.43% | 3.43% |  |  |  |  |  |  |  |  |
Senior Unsecured Notes, 2.45% Due 2036 | Ameren Transmission Company of Illinois | Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  | $ 75,000,000 | $ 75,000,000 | $ 75,000,000 |  |  |  |  |  |  |  |
Long-term debt interest rate |  | 2.45% | 2.45% | 2.45% |  |  |  |  |  |  |  |
Proceeds from Issuance of Unsecured Debt |  |  |  | $ 75,000,000 |  |  |  |  |  |  |  |
Minimum |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share |  |  | $ 90.77 |  |  |  |  |  |  |  |  |
Minimum | Ameren Illinois Company |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Common stock equity to capitalization ratio |  | 30.00% | 30.00% |  |  |  |  |  |  |  |  |
Maximum |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share |  |  | $ 94.80 |  |  |  |  |  |  |  |  |
Weighted Average |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share |  |  | $ 92.91 |  |  |  |  |  |  |  |  |
Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Indexed Shares |  |  |  |  |  | 200,000 |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ 89.31 |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | Forward Sale Agreements Outstanding |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Shares, at Fair Value | 3,400,000 |  |  |  |  |  |  |  |  |  |  |

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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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