Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Segment Reporting Information [Line Items]
External revenues	$ 2,097	$ 1,816
Revenues	2,097	1,816
Fuel and purchased power	(502)	(328)
Natural gas purchased for resale	(169)	(151)
Other operations and maintenance expenses	(485)	(470)
Depreciation and amortization	(367)	(361)
Taxes other than income taxes	(144)	(135)
Other Income, Net	85	89
Interest charges	(175)	(154)
Income taxes	(50)	(44)
Noncontrolling interests - preferred stock dividends	(1)	(1)
Net income attributable to Ameren common shareholders	289	261
Interest income	11	8
Capital expenditures	1,064	890
Union Electric Company
Segment Reporting Information [Line Items]
External revenues	957	775
Fuel and purchased power	(330)	(166)
Natural gas purchased for resale	(30)	(28)
Other operations and maintenance expenses	(250)	(254)
Taxes other than income taxes	(89)	(87)
Other Income, Net	43	44
Interest charges	(60)	(62)
Income taxes	(4)	(1)
Noncontrolling interests - preferred stock dividends	(1)	(1)
Net income attributable to Ameren common shareholders	42	25
Net income available to common shareholder	43	26
Ameren Illinois Company
Segment Reporting Information [Line Items]
External revenues	1,100	1,000
Revenues	1,100	1,000
Purchased Power	(175)	(164)
Natural gas purchased for resale	(139)	(123)
Other operations and maintenance expenses	(236)	(210)
Depreciation and amortization	(159)	(153)
Taxes other than income taxes	(51)	(44)
Other Income, Net	34	31
Interest charges	(62)	(55)
Income taxes	(76)	(67)
Net income attributable to Ameren common shareholders	236	215
Net income available to common shareholder	236	215
Interest income	9	6
Capital expenditures	363	373
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
External revenues	950	768
Revenues	957	775
Fuel and purchased power	(330)	(166)
Natural gas purchased for resale	(30)	(28)
Other operations and maintenance expenses	(250)	(254)
Depreciation and amortization	(194)	(195)
Taxes other than income taxes	(89)	(87)
Other Income, Net	43	44
Interest charges	(60)	(62)
Income taxes	(4)	(1)
Noncontrolling interests - preferred stock dividends	(1)	(1)
Net income attributable to Ameren common shareholders	42	25
Interest income	2	2
Capital expenditures	658	466
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
External revenues	570	506
Revenues	572	506
Fuel and purchased power	(212)	(192)
Natural gas purchased for resale	0	0
Other operations and maintenance expenses	(166)	(136)
Depreciation and amortization	(91)	(93)
Taxes other than income taxes	(21)	(17)
Other Income, Net	23	22
Interest charges	(26)	(22)
Income taxes	(16)	(12)
Noncontrolling interests - preferred stock dividends	0	0
Net income attributable to Ameren common shareholders	63	56
Interest income	8	6
Capital expenditures	167	184
Operating Segments | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
External revenues	411	391
Revenues	411	391
Fuel and purchased power	0	0
Natural gas purchased for resale	(139)	(123)
Other operations and maintenance expenses	(55)	(58)
Depreciation and amortization	(32)	(33)
Taxes other than income taxes	(29)	(26)
Other Income, Net	5	7
Interest charges	(15)	(15)
Income taxes	(38)	(37)
Noncontrolling interests - preferred stock dividends	0	0
Net income attributable to Ameren common shareholders	108	106
Interest income	0	0
Capital expenditures	59	60
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
External revenues	166	151
Revenues	210	185
Fuel and purchased power	0	0
Natural gas purchased for resale	0	0
Other operations and maintenance expenses	(19)	(19)
Depreciation and amortization	(48)	(39)
Taxes other than income taxes	(1)	(2)
Other Income, Net	7	2
Interest charges	(29)	(29)
Income taxes	(31)	(26)
Noncontrolling interests - preferred stock dividends	0	0
Net income attributable to Ameren common shareholders	89	72
Interest income	1	0
Capital expenditures	173	166
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
External revenues	572	506
Revenues	572	506
Purchased Power	(212)	(192)
Other operations and maintenance expenses	(166)	(136)
Depreciation and amortization	(91)	(93)
Taxes other than income taxes	(21)	(17)
Other Income, Net	23	22
Interest charges	(26)	(22)
Income taxes	(16)	(12)
Net income available to common shareholder	63	56
Interest income	8	6
Capital expenditures	167	184
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
External revenues	411	391
Revenues	411	391
Natural gas purchased for resale	(139)	(123)
Other operations and maintenance expenses	(55)	(58)
Depreciation and amortization	(32)	(33)
Taxes other than income taxes	(29)	(26)
Other Income, Net	5	7
Interest charges	(15)	(15)
Income taxes	(38)	(37)
Net income available to common shareholder	108	106
Interest income	0	0
Capital expenditures	59	60
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
External revenues	117	103
Revenues	154	131
Other operations and maintenance expenses	(15)	(16)
Depreciation and amortization	(36)	(27)
Taxes other than income taxes	(1)	(1)
Other Income, Net	6	2
Interest charges	(21)	(18)
Income taxes	(22)	(18)
Net income available to common shareholder	65	53
Interest income	1	0
Capital expenditures	137	129
Other
Segment Reporting Information [Line Items]
Other operations and maintenance expenses	(8)	(14)
Depreciation and amortization	(2)	(1)
Taxes other than income taxes	(4)	(3)
Other Income, Net	8	20
Interest charges	(46)	(32)
Income taxes	39	32
Net income attributable to Ameren common shareholders	(13)	2
Interest income	1	6
Capital expenditures	2	2
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues	(53)	(41)
Revenues	(53)	(41)
Fuel and purchased power	40	30
Natural gas purchased for resale	0	0
Other operations and maintenance expenses	13	11
Depreciation and amortization	0	0
Taxes other than income taxes	0	0
Other Income, Net	(1)	(6)
Interest charges	1	6
Income taxes	0	0
Noncontrolling interests - preferred stock dividends	0	0
Interest income	(1)	(6)
Capital expenditures	5	12
Intersegment Eliminations | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	(7)	(7)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	(2)	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	(44)	(34)
Intersegment Eliminations | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	(37)	(28)
Revenues	(37)	(28)
Purchased Power	(37)	(28)
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	$ (37)	$ (28)