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Rate And Regulatory Matters (Narrative-Federal) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	May 31, 2020	Dec. 31, 2024	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2024
Rate And Regulatory Matters [Line Items]
Capital expenditures				$ 3,118	$ 3,029
Current regulatory liabilities		$ 120		142
Forecast
Rate And Regulatory Matters [Line Items]
Capital expenditures			$ 1,300
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Capital expenditures				1,127	$ 1,091
Current regulatory liabilities		$ 79		101
Midwest Independent Transmission System Operator, Inc | Final Rate Order
Rate And Regulatory Matters [Line Items]
Approved return on equity percentage	10.02%	9.98%
Current regulatory liabilities				7
Midwest Independent Transmission System Operator, Inc | Final Rate Order | Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Current regulatory liabilities				$ 4

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Rate And Regulatory Matters [Line Items]

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The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 13
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-13

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Percentage of public utility's approved return on equity.

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The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 405
-Name Accounting Standards Codification
-Section 25
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477571/980-405-25-1

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