Consolidated Statement of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Other Paid-in Capital:	Retained Earnings:	Deferred Retirement Benefit Costs	Accumulated Other Comprehensive Loss:	Total 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, 2022			$ 6,860	$ 3,646	$ (1)			$ 129					$ 3,111					$ 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 at Dec. 31, 2022	262,000,000.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan	100,000
Shares issued for stock-based compensation	500,000
Common stock shares outstanding at end of period at Mar. 31, 2023	262,600,000
End of period at Mar. 31, 2023	$ 10,736	$ 3	6,861	3,745	(2)	$ (2)		129		$ 511	$ 2,725	$ 80	3,139		$ 0	$ 2,929	$ 49	3,388
Shareholders' equity, end of year at Mar. 31, 2023							$ 10,607		6,455					6,366
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 0.63
Beginning of year at Dec. 31, 2023	$ 11,478		7,216	4,136	(6)			129					3,647					3,756
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			10
Stock-based compensation activity			2
Net income	262								$ 26				26	$ 215				215
Net income attributable to Ameren common shareholders	261			261
Dividends on common stock				(178)
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 at Dec. 31, 2023	266,300,000								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	200,000
Common stock shares outstanding at end of period at Mar. 31, 2024	266,600,000								102,100,000					25,500,000
End of period at Mar. 31, 2024	$ 11,572	$ 3	$ 7,228	$ 4,219	$ (7)	$ (7)		$ 129		$ 511	$ 2,725	$ 80	$ 3,672		$ 0	$ 3,020	$ 49	$ 3,971
Shareholders' equity, end of year at Mar. 31, 2024	$ 11,443						$ 11,443		$ 6,988					$ 7,040
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 0.67