Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information [Line Items]
Operating Revenues	$ 1,693	$ 1,760	$ 3,509	$ 3,822
Net income (loss) attributable to common shareholders	258	237	519	501
Capital expenditures	1,002	891	1,892	1,822
Union Electric Company
Segment Reporting Information [Line Items]
Operating Revenues	888	941	1,663	1,864
Net Income (Loss)	128	102	153	130
Ameren Illinois Company
Segment Reporting Information [Line Items]
Operating Revenues	766	779	1,766	1,880
Net Income (Loss)	124	129	339	327
Capital expenditures	344	437	717	844
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
Operating Revenues	879	933	1,647	1,846
Net Income (Loss)	128	102	153	130
Capital expenditures	638	433	1,104	914
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	509	540	1,015	1,164
Net Income (Loss)	61	66	117	127
Capital expenditures	132	180	316	350
Operating Segments | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Operating Revenues	148	152	539	543
Net Income (Loss)	6	11	112	98
Capital expenditures	59	90	119	141
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
Operating Revenues	157	135	308	269
Net Income (Loss)	79	72	151	143
Capital expenditures	175	197	341	410
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	509	540	1,015	1,164
Net Income (Loss)	61	66	117	127
Capital expenditures	132	180	316	350
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Operating Revenues	148	152	539	543
Net Income (Loss)	6	11	112	98
Capital expenditures	59	90	119	141
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Operating Revenues	109	87	212	173
Net Income (Loss)	57	52	110	102
Capital expenditures	153	167	282	353
Other
Segment Reporting Information [Line Items]
Net Income (Loss)	(16)	(14)	(14)	3
Capital expenditures	2	2	4	5
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues	(43)	(34)	(84)	(73)
Capital expenditures	(4)	(11)	8	2
Intersegment Eliminations | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	(9)	(8)	(16)	(18)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0	0
Intersegment Eliminations | Ameren Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	(34)	(26)	(68)	(55)
Intersegment Eliminations | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	(27)	(26)	(55)	(54)
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	$ (27)	$ (26)	$ (55)	$ (54)