Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information [Line Items]
Operating Revenues	$ 2,060	$ 2,306	$ 5,882	$ 5,911
Net income (loss) attributable to common shareholders	493	452	994	911
Capital expenditures	749	899	2,571	2,437
Union Electric Company
Segment Reporting Information [Line Items]
Operating Revenues	1,237	1,359	3,101	3,096
Net Income (Loss)	411	397	541	547
Ameren Illinois Company
Segment Reporting Information [Line Items]
Operating Revenues	783	904	2,663	2,697
Net Income (Loss)	125	103	452	375
Capital expenditures	382	446	1,226	1,145
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
Operating Revenues	1,228	1,351	3,074	3,071
Net Income (Loss)	411	397	541	547
Capital expenditures	341	431	1,255	1,237
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	557	672	1,721	1,640
Net Income (Loss)	66	51	193	151
Capital expenditures	177	163	527	444
Operating Segments | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Operating Revenues	121	146	664	811
Net Income (Loss)	(5)	(4)	93	82
Capital expenditures	80	114	221	232
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
Operating Revenues	154	137	423	389
Net Income (Loss)	86	78	229	199
Capital expenditures	160	187	570	519
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	558	672	1,722	1,641
Net Income (Loss)	66	51	193	151
Capital expenditures	177	163	527	444
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Operating Revenues	122	146	665	811
Net Income (Loss)	(5)	(4)	93	82
Capital expenditures	80	114	221	232
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Operating Revenues	103	86	276	245
Net Income (Loss)	64	56	166	142
Capital expenditures	125	169	478	469
Other
Segment Reporting Information [Line Items]
Net Income (Loss)	(65)	(70)	(62)	(68)
Capital expenditures	2	1	7	4
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues	(45)	(40)	(118)	(102)
Capital expenditures	(11)	3	(9)	1
Intersegment Eliminations | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	(9)	(8)	(27)	(25)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	(1)	0	(1)	(1)
Intersegment Eliminations | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Intersegment revenues	(1)	0	(1)	0
Intersegment Eliminations | Ameren Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	(34)	(32)	(89)	(76)
Intersegment Eliminations | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	(33)	(31)	(87)	(75)
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	$ (33)	$ (31)	$ (87)	$ (75)