Consolidated Statement of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Other Paid-in Capital	Retained Earnings	Deferred Retirement Benefit Costs	Accumulated Other Comprehensive Income	Total Ameren Corporation Shareholders' Equity	Noncontrolling Interests	Union Electric Company	Union Electric Company Common Stock	Union Electric Company Other Paid-in Capital	Union Electric Company Preferred Stock	Union Electric Company Retained Earnings	Ameren Illinois Company	Ameren Illinois Company Common Stock	Ameren Illinois Company Other Paid-in Capital	Ameren Illinois Company Preferred Stock	Ameren Illinois Company Retained Earnings
Beginning of year at Dec. 31, 2021			$ 6,502	$ 3,182	$ 13			$ 129			$ 2,725		$ 2,595			$ 2,914	$ 49	$ 2,677
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			13
Stock-based compensation activity			(8)
Net income	$ 253								$ 51				51	$ 169				169
Net income attributable to Ameren common shareholders	252			252
Dividends on common stock				(152)
Preferred stock dividends													(1)
Change in deferred retirement benefit costs	1				1
Net income attributable to noncontrolling interest holders	$ (1)							1
Dividends paid to noncontrolling interest holders								(1)
Common stock shares outstanding at beginning of year (in shares) at Dec. 31, 2021	257,700,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan	100,000
Shares issued for stock-based compensation (in shares)	400,000
Common stock shares outstanding at end of period (in shares) at Mar. 31, 2022	258,200,000
End of period at Mar. 31, 2022	$ 9,935	$ 3	6,507	3,282	14	$ 14		129		$ 511		$ 80	2,645		$ 0			2,846
Shareholders' equity, end of year at Mar. 31, 2022							$ 9,806		5,961					5,809
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share (in dollars per share)	$ 0.59
Beginning of year at Dec. 31, 2022	$ 10,637		6,860	3,646	(1)			129			$ 2,725		3,111			$ 2,929	$ 49	3,190
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			12
Stock-based compensation activity			(11)
Net income	265								$ 29				29	$ 198				198
Net income attributable to Ameren common shareholders	264			264
Dividends on common stock				(165)
Preferred stock dividends													(1)
Change in deferred retirement benefit costs	(1)				(1)
Net income attributable to noncontrolling interest holders	$ (1)							1
Dividends paid to noncontrolling interest holders								(1)
Common stock shares outstanding at beginning of year (in shares) at Dec. 31, 2022	262,000,000.0								102,100,000					25,500,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan	100,000
Shares issued for stock-based compensation (in shares)	500,000
Common stock shares outstanding at end of period (in shares) at Mar. 31, 2023	262,600,000								102,100,000					25,500,000
End of period at Mar. 31, 2023	$ 10,736	$ 3	$ 6,861	$ 3,745	$ (2)	$ (2)		$ 129		$ 511		$ 80	$ 3,139		$ 0			$ 3,388
Shareholders' equity, end of year at Mar. 31, 2023	$ 10,607						$ 10,607		$ 6,455					$ 6,366
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share (in dollars per share)	$ 0.63