Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Operating Revenues	$ 1,816	$ 2,062
Net income (loss) attributable to common shareholders	261	264
Capital expenditures	890	931
Union Electric Company
Segment Reporting Information [Line Items]
Operating Revenues	775	923
Net Income (Loss)	25	28
Ameren Illinois Company
Segment Reporting Information [Line Items]
Operating Revenues	1,000	1,101
Net Income (Loss)	215	198
Capital expenditures	373	407
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
Operating Revenues	768	913
Net Income (Loss)	25	28
Capital expenditures	466	481
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	506	624
Net Income (Loss)	56	61
Capital expenditures	184	170
Operating Segments | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Operating Revenues	391	391
Net Income (Loss)	106	87
Capital expenditures	60	51
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
Operating Revenues	151	134
Net Income (Loss)	72	71
Capital expenditures	166	213
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	506	624
Net Income (Loss)	56	61
Capital expenditures	184	170
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Operating Revenues	391	391
Net Income (Loss)	106	87
Capital expenditures	60	51
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Operating Revenues	103	86
Net Income (Loss)	53	50
Capital expenditures	129	186
Other
Segment Reporting Information [Line Items]
Net Income (Loss)	2	17
Capital expenditures	2	3
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues	(41)	(39)
Capital expenditures	12	13
Intersegment Eliminations | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	(7)	(10)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
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	(34)	(29)
Intersegment Eliminations | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	(28)	(28)
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)	$ (28)