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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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Percentage of public utility's requested equity to capital, including debt and equity.

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Amount of public utility's requested rate increase (decrease) with regulatory agency.

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Rate And Regulatory Matters (Narrative-Illinois) (Details) $ in Millions	1 Months Ended			12 Months Ended
	Jan. 31, 2026 USD ($)	Nov. 30, 2025 USD ($)	Oct. 31, 2023 USD ($)	Dec. 31, 2029 USD ($)	Dec. 31, 2028 USD ($)	Dec. 31, 2027 USD ($)	Dec. 31, 2026 USD ($)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Public Utilities, General Disclosures [Line Items]
Capital expenditures								$ 4,128	$ 4,319	$ 3,597
Forecast
Public Utilities, General Disclosures [Line Items]
Capital expenditures							$ 1,300
Ameren Illinois
Public Utilities, General Disclosures [Line Items]
Annual investment in energy-efficiency programs								$ 126
Basis points for ROE modification								0.0200
Capital expenditures								$ 1,481	$ 1,467	$ 1,731
Ameren Illinois \| Forecast
Public Utilities, General Disclosures [Line Items]
Annual investment in energy-efficiency programs				$ 256	$ 222	$ 178
IETL \| Electric Distribution \| Ameren Illinois
Public Utilities, General Disclosures [Line Items]
Multi-year rate plan approved revenue requirement								1,206
Approved rate increase (decrease), amount								308
IETL \| Electric Distribution \| Ameren Illinois \| Forecast
Public Utilities, General Disclosures [Line Items]
Multi-year rate plan approved revenue requirement					$ 1,421	$ 1,367	$ 1,287
Pending Rate Case \| Electric Distribution \| Ameren Illinois
Public Utilities, General Disclosures [Line Items]
Cumulative rate increase								48
Approved rate base								$ 4,200
Percentage of requested equity capital structure								50.00%
Pending Rate Case \| Natural gas \| Ameren Illinois
Public Utilities, General Disclosures [Line Items]
Capital expenditures		$ 75	$ 30
Eligible QIP investments			$ 529
Pending Rate Case \| Electric Energy-Efficiency \| Ameren Illinois
Public Utilities, General Disclosures [Line Items]
Cumulative rate increase		138
Approved rate base		474
Pending Rate Case \| Electric Energy-Efficiency \| Ameren Illinois \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Cumulative rate increase	$ 12
Final Rate Order \| Natural gas \| Ameren Illinois
Public Utilities, General Disclosures [Line Items]
Cumulative rate increase		79
Approved rate base		$ 3,200
Public Utilities, Approved Return on Equity, Percentage		9.60%
Public Utilities, Approved Equity Capital Structure, Percentage		50.00%
Capital expenditures		$ 75