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 period at Dec. 31, 2022			$ 6,860	$ 3,646	$ (1)			$ 129			$ 2,725		$ 3,111					$ 3,190
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			23
Stock-based compensation activity			(3)
Net income	$ 504								$ 132				132	$ 328				328
Net income attributable to Ameren common shareholders	501			501
Dividends on common stock				(330)														0
Preferred stock dividends													(2)					(1)
Change in deferred retirement benefit costs	(2)				(2)
Net income attributable to noncontrolling interest holders	$ (3)							3
Dividends paid to noncontrolling interest holders								(3)
Common stock shares outstanding at beginning of period at Dec. 31, 2022	262,000,000.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan	200,000
Shares issued for stock-based compensation	500,000
Common stock shares outstanding at end of period at Jun. 30, 2023	262,700,000
End of period at Jun. 30, 2023	$ 10,826	$ 3	6,880	3,817	(3)	$ (3)		129		$ 511	2,725	$ 80	3,241		$ 0	$ 2,929	$ 49	3,517
Shareholders' equity, end of year at Jun. 30, 2023							$ 10,697		6,557					6,495
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 1.26
Beginning of period at Mar. 31, 2023			6,861	3,745	(2)			129			2,725		3,139					3,388
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			11
Stock-based compensation activity			8
Net income	$ 239								103				103	130				130
Net income attributable to Ameren common shareholders	237			237
Dividends on common stock				(165)														0
Preferred stock dividends													(1)					(1)
Change in deferred retirement benefit costs	(1)				(1)
Net income attributable to noncontrolling interest holders	$ (2)							2
Dividends paid to noncontrolling interest holders								(2)
Common stock shares outstanding at beginning of period at Mar. 31, 2023	262,600,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan	100,000
Shares issued for stock-based compensation	0
Common stock shares outstanding at end of period at Jun. 30, 2023	262,700,000
End of period at Jun. 30, 2023	$ 10,826	3	6,880	3,817	(3)	(3)		129		511	2,725	80	3,241		0	2,929	49	3,517
Shareholders' equity, end of year at Jun. 30, 2023							10,697		$ 6,557					$ 6,495
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 0.63
Beginning of period at Dec. 31, 2023	$ 11,478		7,216	4,136	(6)			129			2,725		3,647					3,756
Common stock shares outstanding at beginning of period at Dec. 31, 2023	266,300,000								102,100,000					25,500,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued for stock-based compensation	200,000
Common stock shares outstanding at end of period at Mar. 31, 2024	266,600,000
End of period at Mar. 31, 2024			7,228	4,219	(7)			129			2,725		3,672					3,971
Beginning of period at Dec. 31, 2023	$ 11,478		7,216	4,136	(6)			129			2,725		3,647					3,756
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			21
Stock-based compensation activity			9
Net income	522								$ 155				155	$ 340				340
Net income attributable to Ameren common shareholders	519			519
Dividends on common stock				(356)														(25)
Preferred stock dividends													(2)					(1)
Change in deferred retirement benefit costs	(3)				(3)
Net income attributable to noncontrolling interest holders	$ (3)							3
Dividends paid to noncontrolling interest holders								(3)
Common stock shares outstanding at beginning of period 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	300,000
Shares issued for stock-based compensation	200,000
Common stock shares outstanding at end of period at Jun. 30, 2024	266,800,000								102,100,000					25,500,000
End of period at Jun. 30, 2024	$ 11,668	3	7,246	4,299	(9)	(9)		129		511	3,075	80	3,800		0	3,020	49	4,070
Shareholders' equity, end of year at Jun. 30, 2024	$ 11,539						11,539		$ 7,466					$ 7,139
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 1.34
Beginning of period at Mar. 31, 2024			7,228	4,219	(7)			129			2,725		3,672					3,971
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			11
Stock-based compensation activity			7
Net income	$ 260								$ 129				129	$ 125				125
Net income attributable to Ameren common shareholders	258			258
Dividends on common stock				(178)														(25)
Preferred stock dividends													(1)					(1)
Change in deferred retirement benefit costs	(2)				(2)
Net income attributable to noncontrolling interest holders	$ (2)							2
Dividends paid to noncontrolling interest holders								(2)
Common stock shares outstanding at beginning of period at Mar. 31, 2024	266,600,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan	200,000
Shares issued for stock-based compensation	0
Common stock shares outstanding at end of period at Jun. 30, 2024	266,800,000								102,100,000					25,500,000
End of period at Jun. 30, 2024	$ 11,668	$ 3	$ 7,246	$ 4,299	$ (9)	$ (9)		$ 129		$ 511	$ 3,075	$ 80	$ 3,800		$ 0	$ 3,020	$ 49	$ 4,070
Shareholders' equity, end of year at Jun. 30, 2024	$ 11,539						$ 11,539		$ 7,466					$ 7,139
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 0.67