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Supplemental Information (Allowance For Funds Used During Construction) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Allowance for Funds Used During Construction, Rate [Line Items]
Allowance for equity funds used during construction	$ 88	$ 76	$ 54
Allowance for borrowed funds used during construction	52	56	48
Allowance for equity funds used during construction	$ 140	$ 132	$ 102
Ameren Missouri
Allowance for Funds Used During Construction, Rate [Line Items]
Public Utilities, Allowance for Funds Used During Construction, Rate	7.00%	6.00%	6.00%
Allowance for equity funds used during construction	$ 56	$ 58	$ 30
Allowance for borrowed funds used during construction	36	39	27
Allowance for equity funds used during construction	$ 92	$ 97	$ 57
Ameren Illinois
Allowance for Funds Used During Construction, Rate [Line Items]
Public Utilities, Allowance for Funds Used During Construction, Rate	7.00%	6.00%	6.00%
Allowance for equity funds used during construction	$ 30	$ 17	$ 19
Allowance for borrowed funds used during construction	15	15	17
Allowance for equity funds used during construction	$ 45	$ 32	$ 36

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[Line Items] for Allowance for Funds Used During Construction, Rate

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Total increase in earnings in the period representing the cost of equity (based on assumed rate of return) and/or borrowed funds (based on interest rate) used to finance construction of regulated assets, which is expected to be recovered through rate adjustments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

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-Name Accounting Standards Codification
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-SubTopic 360
-Section 25
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The component of the allowance for funds used during construction during the period based on an assumed rate of return on equity funds used in financing the construction of regulated assets.

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Amount capitalized of allowance for funds used during construction.

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Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction.

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