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Long-Term debt and Equity Financings (Details) $ / shares in Units, shares in Millions, $ in Millions | 3 Months Ended | 9 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2024 USD ($) shares | Mar. 31, 2024 USD ($) shares | Sep. 30, 2023 USD ($) shares | Sep. 30, 2024 USD ($) $ / shares shares | Sep. 30, 2023 USD ($) shares | Oct. 31, 2024 USD ($) | Aug. 31, 2024 USD ($) | Jun. 30, 2024 USD ($) | Apr. 30, 2024 USD ($) | Jan. 31, 2024 USD ($)
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Shares issued under the DRPlus and 401(k) plan | shares | 0.1 |  | 0.2 | 0.4 | 0.4 |  |  |  |  |
Issuances of common stock |  |  |  | $ 30.0 | $ 28.0 |  |  |  |  |
Stock Issued During Period, Shares, Other | shares | 0.0 | 0.2 | 0.0 | 0.2 | 0.5 |  |  |  |  |
Stock Issued During Period, Value, Other |  | $ 16.0 |  |  |  |  |  |  |  |
Maximum Value Of Shares To Be Issued Under ATM Program | $ 615.0 |  |  | $ 615.0 |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Basis Spread | 75 |  |  | 75 |  |  |  |  |  |
Minimum |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares |  |  |  | $ 76.69 |  |  |  |  |  |
Maximum |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares |  |  |  | 89.31 |  |  |  |  |  |
Weighted Average |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares |  |  |  | $ 80.96 |  |  |  |  |  |
Dividend reinvestment and 401 (k) plans |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Issuances of common stock | $ 2.0 |  |  | $ 23.0 |  |  |  |  |  |
Accrued Proceeds from Issuance of Common Stock |  |  |  | $ 7.0 |  |  |  |  |  |
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 | shares | 4.7 |  |  | 4.7 |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value | $ 386.0 |  |  | $ 386.0 |  |  |  |  |  |
Period End Net Cash Settlement Price | 29.0 |  |  | 29.0 |  |  |  |  |  |
Period End Net Share Settlement Price | $ 0.3 |  |  | $ 0.3 |  |  |  |  |  |
Forward Sale Agreement Equity Offering Shares | shares | 4.7 |  |  | 4.7 |  |  |  |  |  |
Forward Sale Agreement Gross Sales Price | $ 388.0 |  |  | $ 388.0 |  |  |  |  |  |
Union Electric Company |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Capital contributions from parent |  |  |  | 350.0 | $ 0.0 |  |  |  |  |
Union Electric Company | Other Paid-in Capital: |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Capital contributions from parent | 0.0 |  | $ 0.0 | 350.0 | 0.0 |  |  |  |  |
Union Electric Company | Secured Debt | First Mortgage Bonds, 5.25%, Due 2054 - $350 Issuance |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  |  |  |  |  |  |  |  |  | $ 350.0
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  |  |  | 5.25%
Union Electric Company | Secured Debt | Senior Secured Notes 5.20% Due 2034 |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  |  |  |  |  |  |  |  | $ 500.0 |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  |  | 5.20% |
Union Electric Company | Secured Debt | Senior Secured Notes350 Due2024 |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  |  |  |  |  |  |  |  | $ 350.0 |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  |  | 3.50% |
Union Electric Company | Secured Debt | First Mortgage Bonds, 5.125%, Due 2055 - $450 Issuance | Subsequent Event |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  |  |  |  |  | $ 450.0 |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  | 5.125% |  |  |  |
Ameren Illinois Company |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Capital contributions from parent |  |  |  | 0.0 | 50.0 |  |  |  |  |
Ameren Illinois Company | Other Paid-in Capital: |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Capital contributions from parent | 0.0 |  | $ 50.0 | 0.0 | $ 50.0 |  |  |  |  |
Ameren Illinois Company | Secured Debt | First Mortgage Bonds, 5.55%, Due 2054 - $625 Issuance |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  |  |  |  |  |  |  | $ 625.0 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  | 5.55% |  |
Ameren Transmission Company of Illinois | Unsecured Debt | Senior Unsecured Notes, 5.17%, Due 2039 |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  |  |  |  |  |  | $ 70.0 |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  | 5.17% |  |  |
Ameren Transmission Company of Illinois | Unsecured Debt | Senior Unsecured Notes, 5.42%, Due 2053 |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  |  |  |  |  |  | $ 70.0 |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  | 5.42% |  |  |
Ameren Transmission Company of Illinois | Unsecured Debt | Senior Unsecured Notes, 3.43%, Due 2050 |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  | 3.43% |  |  |
Long-Term Debt, Maturity, Remainder of Fiscal Year |  |  |  |  |  |  | $ 49.0 |  |  |
Ameren (parent) | Unsecured Debt | Senior unsecured Notes 2.50% Due 2024 |  |  |  |  |  |  |  |  |  |
Long-Term Debt And Equity Financings [Line Items] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | $ 450.0 |  |  | $ 450.0 |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 2.50% |  |  | 2.50% |  |  |  |  |  |

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