Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Revenues	$ 2,062	$ 1,879
Net income (loss) attributable to common shareholders	264	252
Capital expenditures	931	774
Union Electric Company
Segment Reporting Information [Line Items]
Revenues	923	818
Net income (loss) attributable to common shareholders	28	50
Ameren Illinois Company
Segment Reporting Information [Line Items]
Revenues	1,101	1,024
Net income (loss) attributable to common shareholders	198	169
Capital expenditures	407	342
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
Revenues	913	808
Net income (loss) attributable to common shareholders	28	50
Capital expenditures	481	414
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Revenues	624	464
Net income (loss) attributable to common shareholders	61	49
Capital expenditures	170	138
Operating Segments | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Revenues	391	481
Net income (loss) attributable to common shareholders	87	80
Capital expenditures	51	49
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
Revenues	134	126
Net income (loss) attributable to common shareholders	71	58
Capital expenditures	213	172
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Revenues	624	465
Net income (loss) attributable to common shareholders	61	49
Capital expenditures	170	138
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Revenues	391	481
Net income (loss) attributable to common shareholders	87	80
Capital expenditures	51	49
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Revenues	86	78
Net income (loss) attributable to common shareholders	50	40
Capital expenditures	186	155
Other
Segment Reporting Information [Line Items]
Net income (loss) attributable to common shareholders	17	15
Capital expenditures	3	2
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues	(39)	(31)
Capital expenditures	13	(1)
Intersegment Eliminations | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	(10)	(10)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	(1)
Intersegment Eliminations | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Intersegment Eliminations | Ameren Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	(29)	(20)
Intersegment Eliminations | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	(28)	(20)
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	$ (28)	$ (20)