Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Reporting Information [Line Items]
Revenues	$ 1,726	$ 1,472	$ 3,605	$ 3,038
Net income (loss) attributable to common shareholders	207	207	459	440
Capital expenditures	764	876	1,538	1,763
Wind generation expenditures		224		417
Union Electric Company
Segment Reporting Information [Line Items]
Revenues	919	809	1,737	1,513
Net income (loss) attributable to common shareholders	100	111	150	158
Wind generation expenditures		224		417
Ameren Illinois Company
Segment Reporting Information [Line Items]
Revenues	769	629	1,793	1,452
Net income (loss) attributable to common shareholders	103	86	272	235
Capital expenditures	357	309	699	646
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
Revenues	912	799	1,720	1,494
Net income (loss) attributable to common shareholders	100	111	150	158
Capital expenditures	392	567	806	1,101
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Revenues	504	386	968	797
Net income (loss) attributable to common shareholders	51	41	100	87
Capital expenditures	143	129	281	286
Operating Segments | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Revenues	184	168	665	515
Net income (loss) attributable to common shareholders	6	8	86	83
Capital expenditures	69	61	118	109
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
Revenues	126	119	252	232
Net income (loss) attributable to common shareholders	63	55	121	102
Capital expenditures	160	131	332	272
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Revenues	504	388	969	799
Net income (loss) attributable to common shareholders	51	41	100	87
Capital expenditures	143	129	281	286
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Revenues	184	168	665	515
Net income (loss) attributable to common shareholders	6	8	86	83
Capital expenditures	69	61	118	109
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Revenues	81	73	159	138
Net income (loss) attributable to common shareholders	46	37	86	65
Capital expenditures	145	119	300	251
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues	(31)	(29)	(62)	(55)
Capital expenditures	(1)	(12)	(2)	(6)
Intersegment Eliminations | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	(7)	(10)	(17)	(19)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	(2)	(1)	(2)
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	(24)	(17)	(44)	(34)
Intersegment Eliminations | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	(24)	(15)	(44)	(31)
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	(24)	(15)	(44)	(31)
Other
Segment Reporting Information [Line Items]
Net income (loss) attributable to common shareholders	(13)	$ (8)	2	10
Capital expenditures	$ 1		$ 3	$ 1