Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) segment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	4
External revenues	$ 6,394	$ 5,794	$ 5,910
Depreciation and amortization	1,146	1,075	995
Interest income	27	29	33
Interest Charges	383	419	381
Income tax benefit	157	155	182
Net Income (Loss) Available to Common Stockholders, Basic	990	871	828
Capital expenditures	3,479	3,233	2,411
Wind generation expenditures	$ 525	564	0
Reportable Subsegments
Segment Reporting Information [Line Items]
External revenues			5,891
Intersubsegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues			19
Union Electric Company
Segment Reporting Information [Line Items]
Number of reportable segments | segment	1
Ameren Illinois Electric Distribution | Ameren Missouri Software Licensing with Ameren Illinois
Segment Reporting Information [Line Items]
Intersegment revenues			14
Ameren Illinois Gas | Ameren Missouri Software Licensing with Ameren Illinois
Segment Reporting Information [Line Items]
Intersegment revenues			5
Ameren Illinois Company
Segment Reporting Information [Line Items]
Number of reportable segments | segment	3
External revenues	$ 2,895	2,535	2,527
Depreciation and amortization	472	434	406
Interest income	1	3	6
Interest Charges	164	155	147
Income tax benefit	143	124	110
Net Income Available to Common Shareholder	425	379	343
Capital expenditures	1,432	1,447	1,208
Ameren Illinois Company | Ameren Missouri Software Licensing with Ameren Illinois
Segment Reporting Information [Line Items]
Intersegment revenues			19
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
External revenues	3,311	3,069	3,212
Depreciation and amortization	632	604	556
Interest income	26	26	26
Interest Charges	137	190	178
Income tax benefit	3	34	68
Net Income Available to Common Shareholder	518	436	426
Capital expenditures	2,015	1,666	1,076
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
External revenues	1,635	1,496	1,487
Depreciation and amortization	309	288	273
Interest income	1	2	6
Interest Charges	74	72	71
Income tax benefit	53	42	45
Net Income Available to Common Shareholder	165	143	146
Capital expenditures	579	543	518
Operating Segments | Ameren Illinois Gas
Segment Reporting Information [Line Items]
External revenues	957	760	791
Depreciation and amortization	90	81	78
Interest income	0	0	0
Interest Charges	42	41	38
Income tax benefit	39	36	30
Net Income Available to Common Shareholder	108	99	84
Capital expenditures	278	301	318
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
External revenues	491	469	401
Depreciation and amortization	111	98	84
Interest income	0	1	1
Interest Charges	83	78	74
Income tax benefit	82	78	64
Net Income Available to Common Shareholder	230	216	185
Capital expenditures	616	716	528
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
External revenues	1,639	1,498	1,504
Depreciation and amortization	309	288	273
Interest income	1	2	6
Interest Charges	74	72	71
Income tax benefit	53	42	45
Net Income Available to Common Shareholder	165	143	146
Capital expenditures	579	543	518
Operating Segments | Ameren Illinois Company | Ameren Illinois Gas
Segment Reporting Information [Line Items]
External revenues	957	760	797
Depreciation and amortization	90	81	78
Interest income	0	0	0
Interest Charges	42	41	38
Income tax benefit	39	36	30
Net Income Available to Common Shareholder	108	99	84
Capital expenditures	278	301	318
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
External revenues	299	277	226
Depreciation and amortization	73	65	55
Interest income	0	1	0
Interest Charges	48	42	38
Income tax benefit	51	46	35
Net Income Available to Common Shareholder	152	137	113
Capital expenditures	575	603	372
Segment Reconciling Items
Segment Reporting Information [Line Items]
Depreciation and amortization	4	4	4
Interest income	3	4	5
Interest Charges	50	42	25
Income tax benefit	(20)	(35)	(25)
Net Income Available to Common Shareholder	(31)	(23)	(13)
Capital expenditures	4	5	3
Intersegment Elimination
Segment Reporting Information [Line Items]
Intersegment revenues	117	96	98
Depreciation and amortization	0	0	0
Interest income	(3)	(4)	(5)
Interest Charges	(3)	(4)	(5)
Income tax benefit	0	0	0
Capital expenditures	(13)	2	(32)
Intersegment Elimination | Ameren Missouri Software Licensing with Ameren Illinois
Segment Reporting Information [Line Items]
Capital expenditures			24
Intersegment Elimination | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	42	40	31
Intersegment Elimination | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	4	2	17
Intersegment Elimination | Ameren Illinois Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	6
Intersegment Elimination | Ameren Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	71	54	63
Intersegment Elimination | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	66	52	62
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	$ 66	$ 52	$ 62