Long-Term Debt And Equity Financings (Narrative) (Details)		1 Months Ended		4 Months Ended		12 Months Ended
	Dec. 31, 2021 USD ($) windGenerationFacility $ / shares shares	Jan. 31, 2022 $ / shares	Oct. 31, 2020 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($) windGenerationFacility $ / shares shares	Dec. 31, 2021 USD ($) windGenerationFacility $ / shares shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares	Jan. 03, 2022 shares	Dec. 30, 2021 shares	Sep. 03, 2021 shares	May 31, 2021 USD ($)	Feb. 11, 2021 USD ($)	Dec. 29, 2020 USD ($)	Oct. 30, 2020 USD ($)	Feb. 03, 2020 USD ($)	Aug. 05, 2019 shares
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, authorized (in shares) | shares	100,000,000				100,000,000	100,000,000
Preferred stock, par value (in dollars per share) | $ / shares	$ 0.01				$ 0.01	$ 0.01
Preferred stock, shares outstanding (in shares) | shares	0				0	0
Shares issued under the DRPlus and 401(k) plan | shares						500,000	700,000	900,000
Issuances of common stock						$ 308,000,000	$ 476,000,000	$ 68,000,000
Stock Issued During Period, Shares, Other | shares						500,000	500,000	800,000
Stock Issued						$ 33,000,000	$ 38,000,000	$ 54,000,000
Common Stock, Shares Authorized Under DRPlus Plan | shares	4,000,000				4,000,000	4,000,000
Common Stock, Shares Authorized Under 401(k) Plan | shares	4,000,000				4,000,000	4,000,000
Maximum Value Of Shares To Be Issued Under ATM Program												$ 750,000,000
Quantity Of Shares Issued Under ATM Program | shares						1,800,000
Value of shares issued under ATM program						$ 148,000,000
Payments of Stock Issuance Costs						$ 2,000,000
Forward Contract Indexed to Issuer's Equity, Indexed Shares | shares																	7,500,000
Initial forward sale price, basis spread	75				75	75
Shares issued under forward sale agreement | shares						1,600,000	5,900,000	0
Common Stock Value Issued Through Forward Sale Agreement													$ 113,000,000	$ 425,000,000
Year One	$ 505,000,000				$ 505,000,000	$ 505,000,000
Debt Default Provision Excess						$ 25,000,000
September 2021 Forward Sale
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Indexed Shares | shares											400,000
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares					$ 87.87
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Shares, at Fair Value | shares	400,000				400,000	400,000
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value	$ 30,000,000				$ 30,000,000	$ 30,000,000
December 2021 Forward Sale
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Indexed Shares | shares										500,000
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares	$ 87.03
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Shares, at Fair Value | shares	500,000				500,000	500,000
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value	$ 41,000,000				$ 41,000,000	$ 41,000,000
Dividend reinvestment and 401 (k) plans [Member]
Long-Term Debt And Equity Financings [Line Items]
Issuances of common stock						$ 47,000,000	$ 51,000,000	$ 68,000,000
Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, authorized (in shares) | shares	7,500,000				7,500,000	7,500,000
Preferred stock, par value (in dollars per share) | $ / shares	$ 1				$ 1	$ 1
Preferred stock, shares outstanding (in shares) | shares	0				0	0
Stock Issued						$ 0	0	0
Year One	$ 55,000,000				$ 55,000,000	$ 55,000,000
Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, authorized (in shares) | shares	2,600,000				2,600,000	2,600,000
Preferred stock, par value (in dollars per share) | $ / shares	$ 0				$ 0	$ 0
Preferred stock, shares outstanding (in shares) | shares	0				0	0
Stock Issued						$ 0	0	0
Year One	$ 400,000,000				$ 400,000,000	400,000,000
Payments for Repurchase of Redeemable Preferred Stock						$ 13,000,000	0	$ 0
Common stock equity to capitalization ratio	54.00%				54.00%	54.00%
Ameren Illinois Company | 6.625% Series
Long-Term Debt And Equity Financings [Line Items]
Payments for Repurchase of Redeemable Preferred Stock						$ 12,000,000
Dividend rate on preferred shares, percentage						6.625%
Ameren Illinois Company | 7.75% Series
Long-Term Debt And Equity Financings [Line Items]
Payments for Repurchase of Redeemable Preferred Stock						$ 1,000,000
Dividend rate on preferred shares, percentage						7.75%
Ameren Missouri and Ameren Illinois
Long-Term Debt And Equity Financings [Line Items]
Bonds interest rate assumption	5.00%				5.00%	5.00%
Dividend rate on preferred shares, percentage						6.00%
Ameren Transmission Company of Illinois
Long-Term Debt And Equity Financings [Line Items]
Year One	$ 50,000,000				$ 50,000,000	$ 50,000,000
Ameren (parent)
Long-Term Debt And Equity Financings [Line Items]
Year One	0				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	0
Long-term debt interest rate	1.75%				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	0
Long-term debt interest rate	1.95%				1.95%	1.95%
Proceeds from Issuance of Unsecured Debt						$ 497,000,000
Senior Secured Notes 3.50% Due 2031 | Ameren (parent) | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 800,000,000				$ 800,000,000	$ 800,000,000	800,000,000
Long-term debt interest rate	3.50%				3.50%	3.50%
Proceeds from Issuance of Unsecured Debt						$ 793,000,000
Senior Unsecured Notes 2.70% due 2020 | Ameren (parent) | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount															$ 350,000,000
Long-term debt interest rate	2.70%				2.70%	2.70%
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	0
Long-term debt interest rate	2.15%				2.15%	2.15%
Proceeds from issuance of secured debt						$ 521,000,000
First Mortgage Bonds, 2.95%, Due 2030 - $465 Issuance | Union Electric Company | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 465,000,000				$ 465,000,000	$ 465,000,000	465,000,000
Long-term debt interest rate	2.95%				2.95%	2.95%
Proceeds from issuance of secured debt						$ 462,000,000
5.00% Senior secured notes due 2020 | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount																$ 85,000,000
5.00% Senior secured notes due 2020 | Union Electric Company | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Long-term debt interest rate	5.00%				5.00%	5.00%
First Mortgage Bonds, 2.625%, Due 2051 - $550 Issuance | Union Electric Company | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 550,000,000				$ 550,000,000	$ 550,000,000	550,000,000
Long-term debt interest rate	2.625%				2.625%	2.625%
Proceeds from issuance of secured debt			$ 543,000,000
Number Of Acquired Wind Generation Facilities | windGenerationFacility	2				2	2
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	0
Long-term debt interest rate	2.90%				2.90%	2.90%
Proceeds from issuance of secured debt						$ 345,000,000
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	0
Long-term debt interest rate	0.375%				0.375%	0.375%
Proceeds from issuance of secured debt						$ 100,000,000
First Mortgage Bonds, 1.55%, Due 2030 | Ameren Illinois Company | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 375,000,000				$ 375,000,000	$ 375,000,000	375,000,000
Long-term debt interest rate	1.55%				1.55%	1.55%
Proceeds from issuance of secured debt						$ 371,000,000
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	0
Long-term debt interest rate	2.45%				2.45%	2.45%
Proceeds from Issuance of Unsecured Debt						$ 75,000,000
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	$ 95,000,000
Long-term debt interest rate	2.96%				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	$ 450,000,000.0				$ 450,000,000.0	$ 450,000,000.0	$ 450,000,000
Year One	$ 50,000,000				$ 50,000,000	$ 50,000,000
Ratio of Indebtedness to Net Capital	0.70				0.70	0.70
Ratio of Indebtedness to Total Assets	0.10				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%	3.43%
Minimum | Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Common stock equity to capitalization ratio	30.00%				30.00%	30.00%
Subsequent Event | January 2022 Forward Sale
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Indexed Shares | shares									200,000
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares		$ 88.10
Subsequent Event | Senior Unsecured Notes, 2.96%, Due 2052 | Ameren Transmission Company of Illinois | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Proceeds from Issuance of Unsecured Debt				$ 95,000,000