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			$ 2,929		$ 3,190
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			35
Stock-based compensation activity			5
Net income	$ 998								$ 544					$ 453
Net income attributable to Ameren common shareholders	994			994
Dividends on common stock				(496)														0
Dividends on preferred stock													(3)					(1)
Change in deferred retirement benefit costs	(3)				(3)
Net income attributable to noncontrolling interest holders	$ (4)							4
Dividends paid to noncontrolling interest holders								(4)
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	400,000
Shares issued for stock-based compensation	500,000
Common stock shares outstanding at end of period at Sep. 30, 2023	262,900,000
End of period at Sep. 30, 2023	$ 11,172	$ 3	6,900	4,144	(4)	$ (4)		129		$ 511	2,725	$ 80	3,652		$ 0	2,979	$ 49	3,642
Shareholders' equity, end of year at Sep. 30, 2023							$ 11,043		6,968					6,670
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 1.89
Beginning of period at Jun. 30, 2023			6,880	3,817	(3)			129			2,725		3,241			2,929		3,517
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			12
Stock-based compensation activity			8
Net income	$ 494								412					125
Net income attributable to Ameren common shareholders	493			493
Dividends on common stock				(166)														0
Dividends on preferred stock													(1)					0
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 period at Jun. 30, 2023	262,700,000
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 Sep. 30, 2023	262,900,000
End of period at Sep. 30, 2023	$ 11,172	3	6,900	4,144	(4)	(4)		129		511	2,725	80	3,652		0	2,979	49	3,642
Shareholders' equity, end of year at Sep. 30, 2023							11,043		6,968					6,670
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			3,020		3,756
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			30
Stock-based compensation activity			18
Net income	979								$ 537					$ 454
Net income attributable to Ameren common shareholders	975			975
Dividends on common stock				(535)														(50)
Dividends on preferred stock													(3)					(1)
Change in deferred retirement benefit costs	(4)				(4)
Net income attributable to noncontrolling interest holders	$ (4)							4
Dividends paid to noncontrolling interest holders								(4)
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	400,000
Shares issued for stock-based compensation	200,000
Common stock shares outstanding at end of period at Sep. 30, 2024	266,900,000								102,100,000					25,500,000
End of period at Sep. 30, 2024	$ 11,962	3	7,264	4,576	(10)	(10)		129		511	3,075	80	4,181		0	3,020	49	4,159
Shareholders' equity, end of year at Sep. 30, 2024	$ 11,833						11,833		$ 7,847					$ 7,228
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 2.01
Beginning of period at Jun. 30, 2024			7,246	4,299	(9)			129			3,075		3,800			3,020		4,070
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			9
Stock-based compensation activity			9
Net income	$ 457								$ 382					$ 114
Net income attributable to Ameren common shareholders	456			456
Dividends on common stock				(179)														(25)
Dividends on preferred stock													(1)					0
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 period at Jun. 30, 2024	266,800,000
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 Sep. 30, 2024	266,900,000								102,100,000					25,500,000
End of period at Sep. 30, 2024	$ 11,962	$ 3	$ 7,264	$ 4,576	$ (10)	$ (10)		$ 129		$ 511	$ 3,075	$ 80	$ 4,181		$ 0	$ 3,020	$ 49	$ 4,159
Shareholders' equity, end of year at Sep. 30, 2024	$ 11,833						$ 11,833		$ 7,847					$ 7,228
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 0.67