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 period at Dec. 31, 2020			$ 6,179	$ 2,757	$ (1)			$ 142			$ 2,518		$ 2,101			$ 2,652	$ 62	$ 2,252
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Settlement of forward sale agreement through common shares issuance			113
Shares issued under the ATM program			121
Shares issued under the DRPlus and 401(k) plan			24
Stock-based compensation activity			(1)
Capital contributions from parent									$ 183		183			$ 70		70
Net income	$ 443								160				160	236				236
Net income attributable to Ameren common shareholders	440			440
Dividends on common stock				(282)
Preferred stock dividends													(2)					(1)
Change in deferred retirement benefit costs	0				0
Net income attributable to noncontrolling interest holders	$ (3)							3
Dividends paid to noncontrolling interest holders								(3)
Redemptions of preferred stock								(13)									(13)
Common stock shares outstanding at beginning of year (in shares) at Dec. 31, 2020	253,300,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under forward sale agreement (in shares)	1,600,000
Stock Issued During Period, Shares, New Issues	1,400,000
Shares issued under the DRPlus and 401(k) plan	300,000
Shares issued for stock-based compensation (in shares)	500,000
Common stock shares outstanding at end of period (in shares) at Jun. 30, 2021	257,100,000
End of period at Jun. 30, 2021	$ 9,482	$ 3	6,436	2,915	(1)	$ (1)		129		$ 511	2,701	$ 80	2,259		$ 0	2,722	49	2,487
Shareholders' equity, end of year at Jun. 30, 2021							$ 9,353		5,551					5,258
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share (in dollars per share)	$ 1.10
Beginning of period at Mar. 31, 2021			6,295	2,850	0			129			2,631		2,148			2,692	49	2,401
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Settlement of forward sale agreement through common shares issuance			0
Shares issued under the ATM program			121
Shares issued under the DRPlus and 401(k) plan			12
Stock-based compensation activity			8
Capital contributions from parent											70					30
Net income	$ 208								112				112	86				86
Net income attributable to Ameren common shareholders	207			207
Dividends on common stock				(142)
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)
Redemptions of preferred stock								0									0
Common stock shares outstanding at beginning of year (in shares) at Mar. 31, 2021	255,500,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under forward sale agreement (in shares)	0
Stock Issued During Period, Shares, New Issues	1,400,000
Shares issued under the DRPlus and 401(k) plan	200,000
Shares issued for stock-based compensation (in shares)	0
Common stock shares outstanding at end of period (in shares) at Jun. 30, 2021	257,100,000
End of period at Jun. 30, 2021	$ 9,482	3	6,436	2,915	(1)	(1)		129		511	2,701	80	2,259		0	2,722	49	2,487
Shareholders' equity, end of year at Jun. 30, 2021							9,353		5,551					5,258
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share (in dollars per share)	$ 0.55
Beginning of period at Dec. 31, 2021	$ 9,829		6,502	3,182	13			129			2,725		2,595			2,914	49	2,677
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Settlement of forward sale agreement through common shares issuance			0
Shares issued under the ATM program			0
Shares issued under the DRPlus and 401(k) plan			25
Stock-based compensation activity			0
Capital contributions from parent									0		0			0		0
Net income	462								$ 152				152	$ 273				273
Net income attributable to Ameren common shareholders	459			459
Dividends on common stock				(305)
Preferred stock dividends													(2)					(1)
Change in deferred retirement benefit costs	1				1
Net income attributable to noncontrolling interest holders	$ (3)							3
Dividends paid to noncontrolling interest holders								(3)
Redemptions of preferred stock								0									0
Common stock shares outstanding at beginning of year (in shares) at Dec. 31, 2021	257,700,000								102,100,000					25,500,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under forward sale agreement (in shares)	0
Stock Issued During Period, Shares, New Issues	0
Shares issued under the DRPlus and 401(k) plan	300,000
Shares issued for stock-based compensation (in shares)	400,000
Common stock shares outstanding at end of period (in shares) at Jun. 30, 2022	258,400,000								102,100,000					25,500,000
End of period at Jun. 30, 2022	$ 10,009	3	6,527	3,336	14	14		129		511	2,725	80	2,745		0	2,914	49	2,949
Shareholders' equity, end of year at Jun. 30, 2022	$ 9,880						9,880		$ 6,061					$ 5,912
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share (in dollars per share)	$ 1.18
Beginning of period at Mar. 31, 2022			6,507	3,282	14			129			2,725		2,645			2,914	49	2,846
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Settlement of forward sale agreement through common shares issuance			0
Shares issued under the ATM program			0
Shares issued under the DRPlus and 401(k) plan			12
Stock-based compensation activity			8
Capital contributions from parent											0					0
Net income	$ 209								$ 101				101	$ 104				104
Net income attributable to Ameren common shareholders	207			207
Dividends on common stock				(153)
Preferred stock dividends													(1)					(1)
Change in deferred retirement benefit costs	0				0
Net income attributable to noncontrolling interest holders	$ (2)							2
Dividends paid to noncontrolling interest holders								(2)
Redemptions of preferred stock								0									0
Common stock shares outstanding at beginning of year (in shares) at Mar. 31, 2022	258,200,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under forward sale agreement (in shares)	0
Stock Issued During Period, Shares, New Issues	0
Shares issued under the DRPlus and 401(k) plan	200,000
Shares issued for stock-based compensation (in shares)	0
Common stock shares outstanding at end of period (in shares) at Jun. 30, 2022	258,400,000								102,100,000					25,500,000
End of period at Jun. 30, 2022	$ 10,009	$ 3	$ 6,527	$ 3,336	$ 14	$ 14		$ 129		$ 511	$ 2,725	$ 80	$ 2,745		$ 0	$ 2,914	$ 49	$ 2,949
Shareholders' equity, end of year at Jun. 30, 2022	$ 9,880						$ 9,880		$ 6,061					$ 5,912
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share (in dollars per share)	$ 0.59