Annual investment in energy-efficiency programs.

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- Definition

Approved rate base

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Multi-year rate plan revenue requirement approved by the ICC.

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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 equity to capital, including debt and equity.

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Amount of public utility's approved rate increase (decrease) by regulatory agency.

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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			6 Months Ended		12 Months Ended
	Jan. 31, 2026	Nov. 30, 2025	Oct. 31, 2023	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2029	Dec. 31, 2028	Dec. 31, 2027	Dec. 31, 2026	Dec. 31, 2025
Rate And Regulatory Matters [Line Items]
Capital expenditures				$ 2,653	$ 2,130
Forecast
Rate And Regulatory Matters [Line Items]
Capital expenditures								$ 700
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Capital expenditures				706	$ 742
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										$ 1,206
Public Utilities, Approved Rate Increase (Decrease), Amount										$ 308
IETL \| Ameren Illinois Company \| Electric Distribution \| Forecast
Rate And Regulatory Matters [Line Items]
Multi-year rate plan approved revenue requirement							$ 1,421	$ 1,367	$ 1,287
Pending Rate Case \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 31
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