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Annual investment in energy-efficiency programs.

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Investments recovered under the QIP that have been challenged in a rate case.

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Revenue requirement for the electric energy-efficiency investment

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Amounts collected from customers to fund the Energy Transition Assistance Fund.

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Costs incurred related to financial assistance programs.

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Natural gas capital investments challenged as imprudent.

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The number or solar generation pilot projects allowed under the CEJA.

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How often a rate case may be filed.

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The return on equity adjustments related to the achievement of certain performance metrics.

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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.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Rate And Regulatory Matters (Narrative-Illinois) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) windGenerationFacility	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 2,954	$ 2,669	$ 2,411
Revenues	6,394	5,794	5,910
Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Capital expenditures	1,432	1,447	1,208
Revenues	2,895	$ 2,535	$ 2,527
Annual investment in energy-efficiency programs	$ 100
Deferred payment arrangement extension	18 months
Financial assistance program costs	$ 4
IETL \| Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Energy Transition Assistance Fund Surcharge	25
Annual investment in energy-efficiency programs	$ 120
IETL \| Electric Distribution \| Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Rate Case Filing Frequency	4 years
Public Utilities, Approved Equity Capital Structure, Percentage	50.00%
Multi-Year Rate Plan Reconciliation Cap	105.00%
Amortization Period	2 years
Amortization Start Date	1 year
IETL \| Electric Distribution \| Ameren Illinois Company \| Minimum
Public Utilities, General Disclosures [Line Items]
Return on Equity Adjustment	0.20%
Public Utilities, Requested Rate Increase (Decrease), Percentage	50.00%
IETL \| Electric Distribution \| Ameren Illinois Company \| Maximum
Public Utilities, General Disclosures [Line Items]
Return on Equity Adjustment	0.60%
IETL \| Electricity, Generation \| Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 20
Number of Solar Generation Pilot Projects \| windGenerationFacility	2
Renewable energy credits and zero emission credits \| Electricity, Generation \| Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Revenues	$ 100
IEIMA revenue requirement reconciliation adjustment \| Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Amortization Period	2 years
Public Utilities, Approved Return on Equity, Percentage	5.80%
Final Rate Order \| Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Electric Energy-Efficiency Revenue Requirement	$ 61
Pending Rate Case \| Natural gas \| Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Natural Gas Capital Investment Prudency Challenge	70
Challenged Recoveries Under the QIP	$ 3
IEIMA revenue requirement reconciliation adjustment \| Final Rate Order \| Electric Distribution \| Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Equity Capital Structure, Percentage	51.00%
Amortization Period	2 years
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 58
FEJA energy-efficiency rider \| Final Rate Order \| Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 10