Long-Term Debt And Equity Financings (Narrative) (Details) - USD ($)		1 Months Ended		12 Months Ended
	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%