Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
Operating Revenues	$ 1,760	$ 1,726	$ 3,822	$ 3,605
Net income (loss) attributable to common shareholders	237	207	501	459
Capital expenditures	891	764	1,822	1,538
Union Electric Company
Segment Reporting Information [Line Items]
Operating Revenues	941	919	1,864	1,737
Net Income (Loss)	102	100	130	150
Ameren Illinois Company
Segment Reporting Information [Line Items]
Operating Revenues	779	769	1,880	1,793
Net Income (Loss)	129	103	327	272
Capital expenditures	437	357	844	699
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
Operating Revenues	933	912	1,846	1,720
Net Income (Loss)	102	100	130	150
Capital expenditures	433	392	914	806
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	540	504	1,164	968
Net Income (Loss)	66	51	127	100
Capital expenditures	180	143	350	281
Operating Segments | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Operating Revenues	152	184	543	665
Net Income (Loss)	11	6	98	86
Capital expenditures	90	69	141	118
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
Operating Revenues	135	126	269	252
Net Income (Loss)	72	63	143	121
Capital expenditures	197	160	410	332
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	540	504	1,164	969
Net Income (Loss)	66	51	127	100
Capital expenditures	180	143	350	281
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Operating Revenues	152	184	543	665
Net Income (Loss)	11	6	98	86
Capital expenditures	90	69	141	118
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Operating Revenues	87	81	173	159
Net Income (Loss)	52	46	102	86
Capital expenditures	167	145	353	300
Other
Segment Reporting Information [Line Items]
Net Income (Loss)	(14)	(13)	3	2
Capital expenditures	2	1	5	3
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues	(34)	(31)	(73)	(62)
Capital expenditures	(11)	(1)	2	(2)
Intersegment Eliminations | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	(8)	(7)	(18)	(17)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0	(1)
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	(26)	(24)	(55)	(44)
Intersegment Eliminations | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	(26)	(24)	(54)	(44)
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	$ (26)	$ (24)	$ (54)	$ (44)