Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) segment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	4
External revenues	$ 7,957	$ 6,394	$ 5,794
Depreciation and amortization	1,289	1,146	1,075
Interest income	35	27	29
Interest Charges	486	383	419
Income tax benefit	176	157	155
Net Income (Loss) Available to Common Stockholders, Basic	1,074	990	871
Capital expenditures	$ 3,351	3,479	3,233
Wind generation expenditures		525	564
Reportable Subsegments
Segment Reporting Information [Line Items]
External revenues			5,794
Intersubsegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues			0
Union Electric Company
Segment Reporting Information [Line Items]
Number of reportable segments | segment	1
Ameren Illinois Company
Segment Reporting Information [Line Items]
Number of reportable segments | segment	3
External revenues	$ 3,756	2,895	2,535
Depreciation and amortization	514	472	434
Interest income	7	1	3
Interest Charges	168	164	155
Income tax benefit	179	143	124
Net Income Attributable to Ameren Common Shareholders	513	425	379
Capital expenditures	1,601	1,432	1,447
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
External revenues	4,012	3,311	3,069
Depreciation and amortization	732	632	604
Interest income	28	26	26
Interest Charges	213	137	190
Income tax benefit	(10)	3	34
Net Income Attributable to Ameren Common Shareholders	562	518	436
Capital expenditures	1,690	2,015	1,666
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
External revenues	2,255	1,635	1,496
Depreciation and amortization	332	309	288
Interest income	7	1	2
Interest Charges	74	74	72
Income tax benefit	68	53	42
Net Income Attributable to Ameren Common Shareholders	202	165	143
Capital expenditures	621	579	543
Operating Segments | Ameren Illinois Gas
Segment Reporting Information [Line Items]
External revenues	1,180	957	760
Depreciation and amortization	98	90	81
Interest income	0	0	0
Interest Charges	44	42	41
Income tax benefit	46	39	36
Net Income Attributable to Ameren Common Shareholders	123	108	99
Capital expenditures	308	278	301
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
External revenues	510	491	469
Depreciation and amortization	123	111	98
Interest income	0	0	1
Interest Charges	84	83	78
Income tax benefit	92	82	78
Net Income Attributable to Ameren Common Shareholders	263	230	216
Capital expenditures	741	616	716
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
External revenues	2,256	1,639	1,498
Depreciation and amortization	332	309	288
Interest income	7	1	2
Interest Charges	74	74	72
Income tax benefit	68	53	42
Net Income Attributable to Ameren Common Shareholders	202	165	143
Capital expenditures	621	579	543
Operating Segments | Ameren Illinois Company | Ameren Illinois Gas
Segment Reporting Information [Line Items]
External revenues	1,180	957	760
Depreciation and amortization	98	90	81
Interest income	0	0	0
Interest Charges	44	42	41
Income tax benefit	46	39	36
Net Income Attributable to Ameren Common Shareholders	123	108	99
Capital expenditures	308	278	301
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
External revenues	320	299	277
Depreciation and amortization	84	73	65
Interest income	0	0	1
Interest Charges	50	48	42
Income tax benefit	65	51	46
Net Income Attributable to Ameren Common Shareholders	188	152	137
Capital expenditures	672	575	603
Segment Reconciling Items
Segment Reporting Information [Line Items]
Depreciation and amortization	4	4	4
Interest income	1	3	4
Interest Charges	72	50	42
Income tax benefit	(20)	(20)	(35)
Net Income Attributable to Ameren Common Shareholders	(76)	(31)	(23)
Capital expenditures	7	4	5
Intersegment Elimination
Segment Reporting Information [Line Items]
Intersegment revenues	140	117	96
Depreciation and amortization	0	0	0
Interest income	(1)	(3)	(4)
Interest Charges	(1)	(3)	(4)
Income tax benefit	0	0	0
Capital expenditures	(16)	(13)	2
Intersegment Elimination | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	34	42	40
Intersegment Elimination | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	1	4	2
Intersegment Elimination | Ameren Illinois Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0
Intersegment Elimination | Ameren Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	105	71	54
Intersegment Elimination | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	104	66	52
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	$ 104	$ 66	$ 52