v3.26.1
Long-Term debt and Equity Financings (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Millions
1 Months Ended 3 Months Ended 6 Months Ended
Jul. 31, 2026
Jun. 30, 2026
Mar. 31, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
May 31, 2026
Feb. 28, 2026
Long-Term Debt And Equity Financings [Line Items]                
Shares issued under the DRPlus and 401(k) plan   100   100 200 200    
Issuances of common stock         $ 22.0 $ 25.0    
Stock Issued During Period, Shares, Other (in shares)   0 200 0 200 300    
Stock Issued During Period, Value, Other     $ 25.0          
Common Stock, Shares Authorized Under Dividend Reinvestment Plan             1,900  
Maximum Value Of Shares To Be Issued Under ATM Program   $ 417.0     $ 417.0      
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Number of Shares Indexed   9,600     9,600      
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share         $ 91.89      
Forward Contract Indexed to Issuer's Equity, Indexed Shares   6,400     6,400      
Gain (Loss) on Extinguishment of Debt   $ 4.0   $ 8.0 $ 4.0 $ 8.0    
Subsequent Event                
Long-Term Debt And Equity Financings [Line Items]                
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Number of Shares Indexed 1,400              
Dividend reinvestment and 401 (k) plans                
Long-Term Debt And Equity Financings [Line Items]                
Issuances of common stock   3.0     15.0      
Accrued Proceeds from Issuance of Common Stock         7.0      
Union Electric Company                
Long-Term Debt And Equity Financings [Line Items]                
Capital contributions from parent   75.0     425.0 $ 0.0    
First Mortgage Bonds 5.00% Due 2036 | Secured Debt | Ameren (parent)                
Long-Term Debt And Equity Financings [Line Items]                
Debt Instrument, Face Amount               $ 400.0
Debt Instrument, Interest Rate, Stated Percentage               5.00%
Senior Unsecured Notes 3.65% Due 2026 | Secured Debt | Ameren (parent)                
Long-Term Debt And Equity Financings [Line Items]                
Debt Instrument, Face Amount               $ 350.0
Debt Instrument, Interest Rate, Stated Percentage               3.65%
Senior Secured Notes and First Mortgage Bonds | Secured Debt | Ameren (parent) | Related Party                
Long-Term Debt And Equity Financings [Line Items]                
Debt Instrument, Repurchase Amount   16.0     16.0      
Gain (Loss) on Extinguishment of Debt         4.0      
First Mortgage Bonds 4.80% Due 2036 | Secured Debt | Union Electric Company                
Long-Term Debt And Equity Financings [Line Items]                
Debt Instrument, Face Amount               $ 450.0
Debt Instrument, Interest Rate, Stated Percentage               4.80%
First Mortgage Bonds 5.55% Due 2056 | Secured Debt | Union Electric Company                
Long-Term Debt And Equity Financings [Line Items]                
Debt Instrument, Face Amount               $ 450.0
Debt Instrument, Interest Rate, Stated Percentage               5.55%
First Mortgage Bonds 5.75% Due 2056 | Debt securities: | Union Electric Company                
Long-Term Debt And Equity Financings [Line Items]                
Debt Instrument, Face Amount   $ 500.0     $ 500.0      
Debt Instrument, Interest Rate, Stated Percentage   5.75%     5.75%      
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   16,000     16,000      
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value   $ 1,600.0     $ 1,600.0      
Period End Net Cash Settlement Price   171.0     171.0      
Period End Net Share Settlement Price   $ 1.5     $ 1.5      
Forward Sale Agreement Equity Offering Shares   16,000     16,000      
Forward Sale Agreement Gross Sales Price   $ 1,600.0     $ 1,600.0      
Minimum                
Long-Term Debt And Equity Financings [Line Items]                
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share         $ 106.32      
Maximum                
Long-Term Debt And Equity Financings [Line Items]                
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share         112.91      
Weighted Average                
Long-Term Debt And Equity Financings [Line Items]                
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share         $ 109.64      
Weighted Average | Subsequent Event                
Long-Term Debt And Equity Financings [Line Items]                
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share $ 112.62