Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Operating Revenues	$ 2,173	$ 2,060	$ 5,682	$ 5,882
Net income (loss) attributable to common shareholders	456	493	975	994
Capital expenditures	1,137	749	3,029	2,571
Union Electric Company
Segment Reporting Information [Line Items]
Operating Revenues	1,342	1,237	3,005	3,101
Net Income (Loss)	381	411	534	541
Ameren Illinois Company
Segment Reporting Information [Line Items]
Operating Revenues	793	783	2,559	2,663
Net Income (Loss)	114	125	453	452
Capital expenditures	374	382	1,091	1,226
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
Operating Revenues	1,333	1,228	2,980	3,074
Net Income (Loss)	381	411	534	541
Capital expenditures	735	341	1,839	1,255
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	551	557	1,566	1,721
Net Income (Loss)	56	66	173	193
Capital expenditures	152	177	468	527
Operating Segments | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Operating Revenues	121	121	660	664
Net Income (Loss)	(10)	(5)	102	93
Capital expenditures	83	80	202	221
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
Operating Revenues	168	154	476	423
Net Income (Loss)	90	86	241	229
Capital expenditures	174	160	515	570
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	552	558	1,567	1,722
Net Income (Loss)	56	66	173	193
Capital expenditures	152	177	468	527
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Operating Revenues	121	122	660	665
Net Income (Loss)	(10)	(5)	102	93
Capital expenditures	83	80	202	221
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Operating Revenues	120	103	332	276
Net Income (Loss)	68	64	178	166
Capital expenditures	139	125	421	478
Other
Segment Reporting Information [Line Items]
Net Income (Loss)	(61)	(65)	(75)	(62)
Capital expenditures	2	2	6	7
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues	(52)	(45)	(136)	(118)
Capital expenditures	(9)	(11)	(1)	(9)
Intersegment Eliminations | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	(9)	(9)	(25)	(27)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	(1)	(1)	(1)	(1)
Intersegment Eliminations | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	(1)	0	(1)
Intersegment Eliminations | Ameren Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	(42)	(34)	(110)	(89)
Intersegment Eliminations | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	(35)	(33)	(90)	(87)
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	$ (35)	$ (33)	$ (90)	$ (87)