Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	4
External revenues	$ 7,500	$ 7,957	$ 6,394
Depreciation and amortization	1,387	1,289	1,146
Interest income	33	35	27
Interest Charges	566	486	383
Income tax benefit	183	176	157
Net Income (Loss) Available to Common Stockholders, Basic	1,152	1,074	990
Capital expenditures	$ 3,597	3,351	3,479
Ameren Missouri
Segment Reporting Information [Line Items]
Number of reportable segments | segment	1
Ameren Illinois
Segment Reporting Information [Line Items]
Number of reportable segments | segment	3
External revenues	$ 3,482	3,756	2,895
Depreciation and amortization	556	514	472
Interest income	21	7	1
Interest Charges	204	168	164
Income tax benefit	209	179	143
Net Income Attributable to Ameren Common Shareholders	607	513	425
Capital expenditures	1,731	1,601	1,432
Operating Segments | Ameren Missouri
Segment Reporting Information [Line Items]
External revenues	3,825	4,012	3,311
Depreciation and amortization	783	732	632
Interest income	11	28	26
Interest Charges	227	213	137
Income tax benefit	(8)	(10)	3
Net Income Attributable to Ameren Common Shareholders	545	562	518
Capital expenditures	1,760	1,690	2,015
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
External revenues	2,217	2,255	1,635
Depreciation and amortization	351	332	309
Interest income	19	7	1
Interest Charges	89	74	74
Income tax benefit	82	68	53
Net Income Attributable to Ameren Common Shareholders	258	202	165
Capital expenditures	752	621	579
Operating Segments | Ameren Illinois Gas
Segment Reporting Information [Line Items]
External revenues	897	1,180	957
Depreciation and amortization	108	98	90
Interest income	1	0	0
Interest Charges	55	44	42
Income tax benefit	50	46	39
Net Income Attributable to Ameren Common Shareholders	134	123	108
Capital expenditures	299	308	278
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
External revenues	561	510	491
Depreciation and amortization	138	123	111
Interest income	2	0	0
Interest Charges	96	84	83
Income tax benefit	106	92	82
Net Income Attributable to Ameren Common Shareholders	296	263	230
Capital expenditures	804	741	616
Operating Segments | Ameren Illinois | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
External revenues	2,218	2,256	1,639
Depreciation and amortization	351	332	309
Interest income	19	7	1
Interest Charges	89	74	74
Income tax benefit	82	68	53
Net Income Attributable to Ameren Common Shareholders	258	202	165
Capital expenditures	752	621	579
Operating Segments | Ameren Illinois | Ameren Illinois Gas
Segment Reporting Information [Line Items]
External revenues	897	1,180	957
Depreciation and amortization	108	98	90
Interest income	1	0	0
Interest Charges	55	44	42
Income tax benefit	50	46	39
Net Income Attributable to Ameren Common Shareholders	134	123	108
Capital expenditures	299	308	278
Operating Segments | Ameren Illinois | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
External revenues	367	320	299
Depreciation and amortization	97	84	73
Interest income	1	0	0
Interest Charges	60	50	48
Income tax benefit	77	65	51
Net Income Attributable to Ameren Common Shareholders	215	188	152
Capital expenditures	680	672	575
Segment Reconciling Items
Segment Reporting Information [Line Items]
Depreciation and amortization	7	4	4
Interest income	5	1	3
Interest Charges	104	72	50
Income tax benefit	(47)	(20)	(20)
Net Income Attributable to Ameren Common Shareholders	(81)	(76)	(31)
Capital expenditures	9	7	4
Intersegment Elimination
Segment Reporting Information [Line Items]
Intersegment revenues	151	140	117
Depreciation and amortization	0	0	0
Interest income	(5)	(1)	(3)
Interest Charges	(5)	(1)	(3)
Income tax benefit	0	0	0
Capital expenditures	(27)	(16)	(13)
Intersegment Elimination | Ameren Missouri
Segment Reporting Information [Line Items]
Intersegment revenues	34	34	42
Intersegment Elimination | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	1	1	4
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	116	105	71
Intersegment Elimination | Ameren Illinois
Segment Reporting Information [Line Items]
Intersegment revenues	113	104	66
Intersegment Elimination | Ameren Illinois | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0
Intersegment Elimination | Ameren Illinois | Ameren Illinois Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0
Intersegment Elimination | Ameren Illinois | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	$ 113	$ 104	$ 66