Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Segment Reporting Information [Line Items]
Revenues	$ 2,306	$ 1,811	$ 5,911	$ 4,849
Net income (loss) attributable to common shareholders	452	425	911	865
Capital expenditures	899	850	2,437	2,613
Wind generation expenditures		98		515
Union Electric Company
Segment Reporting Information [Line Items]
Revenues	1,359	1,129	3,096	2,642
Net income (loss) attributable to common shareholders	397	375	547	533
Wind generation expenditures		98		515
Ameren Illinois Company
Segment Reporting Information [Line Items]
Revenues	904	645	2,697	2,097
Net income (loss) attributable to common shareholders	103	79	375	314
Capital expenditures	446	380	1,145	1,026
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
Revenues	1,351	1,118	3,071	2,612
Net income (loss) attributable to common shareholders	397	375	547	533
Capital expenditures	431	466	1,237	1,567
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Revenues	672	425	1,640	1,222
Net income (loss) attributable to common shareholders	51	36	151	123
Capital expenditures	163	143	444	429
Operating Segments | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Revenues	146	127	811	642
Net income (loss) attributable to common shareholders	(4)	(8)	82	75
Capital expenditures	114	93	232	202
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
Revenues	137	141	389	373
Net income (loss) attributable to common shareholders	78	73	199	175
Capital expenditures	187	154	519	426
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Revenues	672	428	1,641	1,227
Net income (loss) attributable to common shareholders	51	36	151	123
Capital expenditures	163	143	444	429
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Revenues	146	127	811	642
Net income (loss) attributable to common shareholders	(4)	(8)	82	75
Capital expenditures	114	93	232	202
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Revenues	86	90	245	228
Net income (loss) attributable to common shareholders	56	51	142	116
Capital expenditures	169	144	469	395
Other
Segment Reporting Information [Line Items]
Net income (loss) attributable to common shareholders	(70)	(51)	(68)	(41)
Capital expenditures	1	2	4	3
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues	(40)	(33)	(102)	(88)
Capital expenditures	3	(8)	1	(14)
Intersegment Eliminations | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	(8)	(11)	(25)	(30)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	(3)	(1)	(5)
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	(32)	(19)	(76)	(53)
Intersegment Eliminations | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	(31)	(18)	(75)	(49)
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	$ (31)	$ (18)	$ (75)	$ (49)