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 (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, 2021			$ 6,502	$ 3,182	$ 13			$ 129					$ 2,595			$ 2,914		$ 2,677
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			37
Capital contributions from parent														$ 0		0
Stock-based compensation activity			9
Net income	$ 915								$ 550				550	376				376
Net income attributable to Ameren common shareholders	911			911
Dividends on common stock				(457)
Preferred stock dividends													(3)					(1)
Change in deferred retirement benefit costs	1				1
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, 2021	257,700,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan	400,000
Shares issued for stock-based compensation	400,000
Common stock shares outstanding at end of period at Sep. 30, 2022	258,500,000
End of period at Sep. 30, 2022	$ 10,330	$ 3	6,548	3,636	14	$ 14		129		$ 511	$ 2,725	$ 80	3,142		$ 0	2,914	$ 49	3,052
Shareholders' equity, end of year at Sep. 30, 2022							$ 10,201		6,458					6,015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 1.77
Beginning of period at Jun. 30, 2022			6,527	3,336	14			129					2,745			2,914		2,949
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			12
Capital contributions from parent																0
Stock-based compensation activity			9
Net income	$ 453								398				398	103				103
Net income attributable to Ameren common shareholders	452			452
Dividends on common stock				(152)
Preferred stock dividends													(1)					0
Change in deferred retirement benefit costs	0				0
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, 2022	258,400,000
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, 2022	258,500,000
End of period at Sep. 30, 2022	$ 10,330	3	6,548	3,636	14	14		129		511	2,725	80	3,142		0	2,914	49	3,052
Shareholders' equity, end of year at Sep. 30, 2022							10,201		6,458					6,015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 0.59
Beginning of period at Dec. 31, 2022	$ 10,637		6,860	3,646	(1)			129					3,111			2,929		3,190
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			35
Capital contributions from parent														50		50
Stock-based compensation activity			5
Net income	998								$ 544				544	$ 453				453
Net income attributable to Ameren common shareholders	994			994
Dividends on common stock				(496)
Preferred stock dividends													(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								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	500,000
Common stock shares outstanding at end of period at Sep. 30, 2023	262,900,000								102,100,000					25,500,000
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						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					3,241			2,929		3,517
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			12
Capital contributions from parent																50
Stock-based compensation activity			8
Net income	$ 494								$ 412				412	$ 125				125
Net income attributable to Ameren common shareholders	493			493
Dividends on common stock				(166)
Preferred stock dividends													(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								102,100,000					25,500,000
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						$ 11,043		$ 6,968					$ 6,670
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 0.63