Annual investment in energy-efficiency programs.

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Approved rate base

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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 equity to capital, including debt and equity.

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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) - USD ($) $ in Millions	1 Months Ended			3 Months Ended	9 Months Ended		12 Months Ended
	Jan. 31, 2026	Nov. 30, 2025	Oct. 31, 2023	Mar. 31, 2028	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2029	Dec. 31, 2028	Dec. 31, 2027	Dec. 31, 2026	Dec. 31, 2025	Dec. 31, 2024
Rate And Regulatory Matters [Line Items]
Capital expenditures					$ 4,089	$ 3,118
Forecast
Rate And Regulatory Matters [Line Items]
Capital expenditures				$ 1,200
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Capital expenditures					1,088	$ 1,127
Ameren Illinois Company \| Forecast
Rate And Regulatory Matters [Line Items]
Annual investment in energy-efficiency programs							$ 276	$ 239	$ 192
IETL \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Multi-year rate plan approved revenue requirement											$ 1,287	$ 1,206
IETL \| Ameren Illinois Company \| Electric Distribution \| Forecast
Rate And Regulatory Matters [Line Items]
Multi-year rate plan approved revenue requirement									$ 1,421	$ 1,367
Pending Rate Case \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount					$ 28
Public Utilities, Requested Equity Capital Structure, Percentage					50.00%
Pending Rate Case \| Ameren Illinois Company \| Natural gas
Rate And Regulatory Matters [Line Items]
Capital expenditures	$ 75		$ 30
Eligible QIP investments			$ 529
Final Rate Order \| Ameren Illinois Company \| Natural gas
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 79
Approved return on equity percentage		9.60%
Public Utilities, Approved Equity Capital Structure, Percentage		50.00%
Approved rate base		$ 3,200
Capital expenditures		$ 75