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