Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Revenues	$ 1,879	$ 1,566
Net income (loss) attributable to common shareholders	252	233
Capital expenditures	774	887
Wind generation expenditures	0	193
Union Electric Company
Segment Reporting Information [Line Items]
Revenues	818	704
Net income (loss) attributable to common shareholders	50	47
Wind generation expenditures	0	193
Ameren Illinois Company
Segment Reporting Information [Line Items]
Revenues	1,024	823
Net income (loss) attributable to common shareholders	169	149
Capital expenditures	342	337
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
Revenues	808	695
Net income (loss) attributable to common shareholders	50	47
Capital expenditures	414	534
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Revenues	464	411
Net income (loss) attributable to common shareholders	49	46
Capital expenditures	138	157
Operating Segments | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Revenues	481	347
Net income (loss) attributable to common shareholders	80	75
Capital expenditures	49	48
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
Revenues	126	113
Net income (loss) attributable to common shareholders	58	47
Capital expenditures	172	141
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Revenues	465	411
Net income (loss) attributable to common shareholders	49	46
Capital expenditures	138	157
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Revenues	481	347
Net income (loss) attributable to common shareholders	80	75
Capital expenditures	49	48
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Revenues	78	65
Net income (loss) attributable to common shareholders	40	28
Capital expenditures	155	132
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues	(31)	(26)
Capital expenditures	(1)	6
Intersegment Eliminations | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	(10)	(9)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	(1)	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	(20)	(17)
Intersegment Eliminations | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	(20)	(16)
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	(20)	(16)
Other
Segment Reporting Information [Line Items]
Net income (loss) attributable to common shareholders	15	18
Capital expenditures	$ 2	$ 1