Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) segment	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	4
External revenues	$ 7,623	$ 7,500	$ 7,957
Revenues	7,623	7,500	7,957
Fuel and purchased power	(1,681)	(1,812)	(2,020)
Natural gas purchased for resale	(320)	(355)	(657)
Other operations and maintenance	(1,969)	(1,866)	(1,937)
Depreciation and amortization	(1,590)	(1,387)	(1,289)
Taxes other than income taxes	(547)	(522)	(539)
Other Income, Net	417	348	226
Interest Charges	(663)	(566)	(486)
Income tax benefit	(83)	(183)	(176)
Preferred Stock Dividends	(5)	(5)	(5)
Net Income (Loss) Available to Common Stockholders, Basic	1,182	1,152	1,074
Interest income	41	33	35
Capital expenditures	$ 4,319	3,597	3,351
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	$ 3,472	3,482	3,756
Revenues	3,472	3,482	3,756
Purchased power	621	820	880
Natural gas purchased for resale	(260)	(276)	(553)
Other operations and maintenance	(906)	(818)	(882)
Depreciation and amortization	(619)	(556)	(514)
Taxes other than income taxes	(157)	(146)	(161)
Other Income, Net	147	156	96
Interest Charges	(241)	(204)	(168)
Income tax benefit	(193)	(209)	(179)
Preferred Stock Dividends	(2)	(2)	(2)
Net Income (Loss) Available to Common Stockholders, Basic	620	607	513
Interest income	32	21	7
Capital expenditures	1,467	1,731	1,601
Operating Segments | Ameren Missouri
Segment Reporting Information [Line Items]
External revenues	3,960	3,825	4,012
Revenues	3,993	3,859	4,046
Fuel and purchased power	(1,071)	(997)	(1,150)
Natural gas purchased for resale	(60)	(79)	(104)
Other operations and maintenance	(1,050)	(1,003)	(1,028)
Depreciation and amortization	(917)	(783)	(732)
Taxes other than income taxes	(372)	(360)	(363)
Other Income, Net	196	130	99
Interest Charges	(244)	(227)	(213)
Income tax benefit	87	8	10
Preferred Stock Dividends	(3)	(3)	(3)
Net Income (Loss) Available to Common Stockholders, Basic	559	545	562
Interest income	8	11	28
Capital expenditures	2,712	1,760	1,690
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
External revenues	2,088	2,217	2,255
Revenues	2,089	2,218	2,256
Fuel and purchased power	(740)	(933)	(984)
Natural gas purchased for resale	0	0	0
Other operations and maintenance	(619)	(532)	(580)
Depreciation and amortization	(369)	(351)	(332)
Taxes other than income taxes	(75)	(75)	(75)
Other Income, Net	97	103	60
Interest Charges	(98)	(89)	(74)
Income tax benefit	(50)	(82)	(68)
Preferred Stock Dividends	(1)	(1)	(1)
Net Income (Loss) Available to Common Stockholders, Basic	234	258	202
Interest income	28	19	7
Capital expenditures	579	752	621
Operating Segments | Ameren Illinois Gas
Segment Reporting Information [Line Items]
External revenues	938	897	1,180
Revenues	938	897	1,180
Fuel and purchased power	0	0	0
Natural gas purchased for resale	(260)	(276)	(553)
Other operations and maintenance	(230)	(237)	(253)
Depreciation and amortization	(129)	(108)	(98)
Taxes other than income taxes	(78)	(67)	(82)
Other Income, Net	27	30	19
Interest Charges	(63)	(55)	(44)
Income tax benefit	(56)	(50)	(46)
Preferred Stock Dividends	0	0	0
Net Income (Loss) Available to Common Stockholders, Basic	149	134	123
Interest income	1	1	0
Capital expenditures	264	299	308
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
External revenues	637	561	510
Revenues	781	677	615
Fuel and purchased power	0	0	0
Natural gas purchased for resale	0	0	0
Other operations and maintenance	(70)	(60)	(60)
Depreciation and amortization	(167)	(138)	(123)
Taxes other than income taxes	(9)	(8)	(9)
Other Income, Net	26	28	17
Interest Charges	(117)	(96)	(84)
Income tax benefit	(120)	(106)	(92)
Preferred Stock Dividends	(1)	(1)	(1)
Net Income (Loss) Available to Common Stockholders, Basic	323	296	263
Interest income	6	2	0
Capital expenditures	758	804	741
Operating Segments | Ameren Illinois | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
External revenues	2,089	2,218	2,256
Revenues	2,089	2,218	2,256
Purchased power	740	933	984
Other operations and maintenance	(619)	(532)	(580)
Depreciation and amortization	(369)	(351)	(332)
Taxes other than income taxes	(75)	(75)	(75)
Other Income, Net	97	103	60
Interest Charges	(98)	(89)	(74)
Income tax benefit	(50)	(82)	(68)
Preferred Stock Dividends	(1)	(1)	(1)
Net Income (Loss) Available to Common Stockholders, Basic	234	258	202
Interest income	28	19	7
Capital expenditures	579	752	621
Operating Segments | Ameren Illinois | Ameren Illinois Gas
Segment Reporting Information [Line Items]
External revenues	938	897	1,180
Revenues	938	897	1,180
Natural gas purchased for resale	(260)	(276)	(553)
Other operations and maintenance	(230)	(237)	(253)
Depreciation and amortization	(129)	(108)	(98)
Taxes other than income taxes	(78)	(67)	(82)
Other Income, Net	27	30	19
Interest Charges	(63)	(55)	(44)
Income tax benefit	(56)	(50)	(46)
Net Income (Loss) Available to Common Stockholders, Basic	149	134	123
Interest income	1	1	0
Capital expenditures	264	299	308
Operating Segments | Ameren Illinois | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
External revenues	445	367	320
Revenues	564	480	424
Other operations and maintenance	(57)	(49)	(49)
Depreciation and amortization	(121)	(97)	(84)
Taxes other than income taxes	(4)	(4)	(4)
Other Income, Net	23	23	17
Interest Charges	(80)	(60)	(50)
Income tax benefit	(87)	(77)	(65)
Preferred Stock Dividends	(1)	(1)	(1)
Net Income (Loss) Available to Common Stockholders, Basic	237	215	188
Interest income	3	1	0
Capital expenditures	624	680	672
Segment Reconciling Items
Segment Reporting Information [Line Items]
Other operations and maintenance	(48)	(67)	(42)
Depreciation and amortization	(8)	(7)	(4)
Taxes other than income taxes	(13)	(12)	(10)
Other Income, Net	83	62	32
Interest Charges	(153)	(104)	(72)
Income tax benefit	56	47	20
Net Income (Loss) Available to Common Stockholders, Basic	(83)	(81)	(76)
Interest income	10	5	1
Capital expenditures	7	9	7
Intersegment Elimination
Segment Reporting Information [Line Items]
Intersegment revenues	178	151	140
Revenues	(178)	(151)	(140)
Fuel and purchased power	130	118	114
Natural gas purchased for resale	0	0	0
Other operations and maintenance	48	33	26
Depreciation and amortization	0	0	0
Taxes other than income taxes	0	0	0
Other Income, Net	(12)	(5)	(1)
Interest Charges	12	5	1
Income tax benefit	0	0	0
Preferred Stock Dividends	0	0	0
Interest income	(12)	(5)	(1)
Capital expenditures	(1)	(27)	(16)
Intersegment Elimination | Ameren Missouri
Segment Reporting Information [Line Items]
Intersegment revenues	33	34	34
Intersegment Elimination | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	1	1	1
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	144	116	105
Intersegment Elimination | Ameren Illinois
Segment Reporting Information [Line Items]
Intersegment revenues	119	113	104
Revenues	(119)	(113)	(104)
Purchased power	119	113	104
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	$ 119	$ 113	$ 104