Long-Term Debt And Equity Financings (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended
	Jan. 31, 2025	Jan. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Oct. 31, 2024	Sep. 30, 2024	Aug. 31, 2024	Jun. 30, 2024	Apr. 30, 2024	Jan. 31, 2024	Nov. 30, 2023	Jun. 30, 2023	May 31, 2023	Mar. 31, 2023	May 31, 2022	May 31, 2021
Long-Term Debt And Equity Financings [Line Items]
Gain (Loss) on Extinguishment of Debt			$ 16.0	$ 0.0	$ 0.0
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			500,000	600,000	500,000
Issuances of common stock			$ 273.0	$ 346.0	$ 333.0
Accrued Proceeds from Issuance of Common Stock			$ 7.0	$ 7.0
Shares issued (in shares)			200,000	500,000	400,000
Value of stock issued				$ 40.0
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			$ 550.0														$ 1,750.0
Number of shares issued under ATM Program (in shares)			2,900,000	3,200,000	3,400,000
Value of shares issued under ATM program			$ 233.0	$ 299.0	$ 292.0
Payments of stock issuance costs			$ 2.0	3.0	3.0
Initial forward sale price, basis spread			0.0075
Termination of a financing obligation			$ 0.0	240.0	0.0
Debt default provision excess			$ 25.0
Forward Sale Agreements Outstanding
Long-Term Debt And Equity Financings [Line Items]
Number of shares to settle forward sale agreements (in shares)			2,500,000
Cash settlement of forward sale agreements			$ 213.0
Period End Net Cash Settlement Price			13.0
Period end net share settlement price			0.1
Forward sale agreement equity offering shares (in shares)			2.5
Forward Sale Agreement Gross Sales Price			215.0
Dividend reinvestment and 401 (k) plans
Long-Term Debt And Equity Financings [Line Items]
Issuances of common stock			$ 33.0	39.0	41.0
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		$ 240.0	$ 0.0	240.0	0.0
Ameren Missouri | Secured Debt | Related Party
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount			$ 58.0	0.0
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	0.0	$ 0.0
Common stock equity to capitalization ratio			54.00%
Ameren Illinois | Secured Debt | Related Party
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount			$ 3.0	0.0
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%
Senior Secured Notes and First Mortgage Bonds | Secured Debt | Related Party
Long-Term Debt And Equity Financings [Line Items]
Gain (Loss) on Extinguishment of Debt			$ 16.0
Interest Expense, Debt			1.0
Senior Secured Notes and First Mortgage Bonds | Ameren (parent) | Secured Debt | Related Party
Long-Term Debt And Equity Financings [Line Items]
Repayments of Senior Secured Notes and First Mortgage Bonds			44.0
2.50% Senior unsecured notes due 2024 | Ameren (parent) | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount			$ 0.0	450.0			$ 450.0
Long-term debt interest rate			2.50%				2.50%
5.70% Senior unsecured notes due 2026 | Ameren (parent) | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount			$ 600.0	600.0								$ 600.0
Long-term debt interest rate			5.70%									5.70%
5.00% Senior unsecured notes due 2029 | Ameren (parent) | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount			$ 700.0
Long-term debt interest rate			5.00%
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			$ 350.0	0.0							$ 350.0
Long-term debt interest rate			5.25%								5.25%
Senior Secured Notes 5.20% Due 2034 | Ameren Missouri | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount										$ 500.0
Long-term debt interest rate										5.20%
3.50% senior secured notes due 2024 | Ameren Missouri | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount			$ 0.0	350.0						$ 350.0
Long-term debt interest rate			3.50%							3.50%
First Mortgage Bonds, 5.125%, Due 2055 - $450 Issuance | Ameren Missouri | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount			$ 450.0	0.0		$ 450.0
Long-term debt interest rate			5.125%			5.125%
4.85% Securitized Utility Tariff Bonds Due 2039 | Ameren Missouri | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount			$ 476.0	0.0
Long-term debt interest rate			4.85%
5.45% First mortgage bonds due 2053 | Ameren Missouri | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount			$ 500.0	500.0											$ 500.0
Long-term debt interest rate			5.45%												5.45%
5.55% First mortgage bonds due 2054 | Ameren Illinois | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount			$ 625.0	0.0					$ 625.0
Long-term debt interest rate			5.55%						5.55%
4.95% First mortgage bonds due 2033 | Ameren Illinois | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount			$ 500.0	500.0										$ 500.0
Long-term debt interest rate			4.95%
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%
0.375% First Mortgage bonds due 2023 | Ameren Illinois | Debt securities
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount													$ 100.0
Long-term debt interest rate													0.375%
Senior Unsecured Notes, 5.17%, Due 2039 | Ameren Transmission Company of Illinois | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount			$ 70.0	0.0				$ 70.0
Long-term debt interest rate			5.17%					5.17%
Senior Unsecured Notes, 5.42%, Due 2053 | Ameren Transmission Company of Illinois | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount			$ 70.0	0.0				$ 70.0
Long-term debt interest rate			5.42%					5.42%
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			$ 351.0	$ 400.0
Long-term debt interest rate			3.43%					3.43%
Long-Term Debt, Maturity, Remainder of Fiscal Year								$ 49.0
Ratio of Indebtedness to Net Capital			0.70
Ratio of Indebtedness to Total Assets			0.10
Minimum
Long-Term Debt And Equity Financings [Line Items]
Forward contract indexed to issuer's equity, forward rate per share (in dollars per share)			$ 81.00
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)			$ 93.06
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)			$ 84.14
Subsequent Event | Forward Sale Agreements Outstanding
Long-Term Debt And Equity Financings [Line Items]
Number of shares to settle forward sale agreements (in shares)	600,000
Subsequent Event | 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)	$ 87.43