The equity capital structure included in an administrative law judge's proposed order.

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The rate base included in an administrative law judge's proposed order.

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The return on equity percentage included in an administrative law judge's proposed order.

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Amortization period of a regulatory asset or liability

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

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Electric energy-efficiency rate increase

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ICC required RTO cost benefit study duration

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The electric energy-efficiency rate increase recommended by the ICC staff.

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The equity capital percentage recommend by the ICC staff.

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The rate base recommended by the ICC staff.

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The rate increase recommended by the ICC staff.

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The return on equity percentage recommended by the ICC staff.

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The equity capital structure recommended by intervenors.

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The rate increase recommended by intervenors.

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The return on equity recommended by intervenors.

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The revenue requirement included in an administrative law judge's proposed order.

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The revenue requirement recommended by the ICC staff.

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Multi-Year Rate Plan Reconciliation Cap

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Ameren Illinois' requested multi-year rate plan revenue requirement.

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Natural gas capital investments challenged as imprudent

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Number of Performance Metrics

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Rate And Regulatory Matters [Line Items]

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Value established for a utility on which the entity is allowed to earn a particular rate of return

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No definition available.

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The return on equity adjustments related to the achievement of certain performance metrics requested by Ameren Illinois.

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

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Percentage of public utility's requested return on equity.

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- Definition

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	3 Months Ended			9 Months Ended		12 Months Ended
	Dec. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) numberOfProposedPerformanceMetrics	Sep. 30, 2022 USD ($)	Dec. 31, 2027 USD ($)	Dec. 31, 2026 USD ($)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Rate And Regulatory Matters [Line Items]
Revenues		$ 2,060	$ 2,306	$ 5,882	$ 5,911
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Revenues		$ 783	$ 904	$ 2,663	$ 2,697
Ameren Illinois Company \| Maximum
Rate And Regulatory Matters [Line Items]
ICC required RTO cost benefit study duration				10 years
Ameren Illinois Company \| Minimum
Rate And Regulatory Matters [Line Items]
ICC required RTO cost benefit study duration				5 years
Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Requested Return on Equity Adjustment				0.24%
Number of Performance Metrics \| numberOfProposedPerformanceMetrics				7
IETL \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
ICC recommended return on equity percentage				5.80%	8.90%
Public Utilities, Approved Equity Capital Structure, Percentage				50.00%
Amortization Period				2 years
Amortization Start Date				1 year
Multi-Year Rate Plan Reconciliation Cap				105.00%
IETL \| Ameren Illinois Company \| Electric Distribution \| Forecast
Rate And Regulatory Matters [Line Items]
Multi-year rate plan requested revenue requirement						$ 1,556	$ 1,480	$ 1,385	$ 1,289
Public Utilities, Requested Return on Equity, Percentage	9.85%					10.50%	10.50%	10.50%	10.50%
Public Utilities, Requested Equity Capital Structure, Percentage	52.00%					54.03%	54.02%	53.97%	53.99%
Rate Base						$ 5,200	$ 4,900	$ 4,600	$ 4,300
Multi-year rate plan ICC staff recommended revenue requirement						$ 1,435	$ 1,383	$ 1,295	$ 1,211
ICC recommended return on equity percentage						8.90%	8.90%	8.90%	8.90%
ICC staff recommended equity capital structure						50.00%	50.00%	50.00%	50.00%
ICC staff recommended rate base						$ 4,800	$ 4,600	$ 4,400	$ 4,100
Multi-year rate plan ALJ proposed revenue requirement						$ 1,450	$ 1,389	$ 1,306	$ 1,219
ALJ proposed return on equity percentage						9.24%	9.24%	9.24%	9.24%
ALJ proposed equity capital structure						50.00%	50.00%	50.00%	50.00%
ALJ proposed rate base						$ 4,800	$ 4,600	$ 4,400	$ 4,100
Public Utilities, Requested Rate Increase (Decrease), Percentage							50.00%
Public Utilities, Requested Rate Increase (Decrease), Amount									$ 177
IETL \| Ameren Illinois Company \| Electric Distribution \| Maximum \| Forecast
Rate And Regulatory Matters [Line Items]
ALJ proposed equity capital structure	50.00%
IETL \| Ameren Illinois Company \| Electric Distribution \| Minimum
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Percentage				50.00%
Pending Rate Case \| Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Electric energy-efficiency rate increase				$ 27
ICC staff recommended electric energy-efficiency rate increase				$ 24
Pending Rate Case \| Ameren Illinois Company \| Electric Distribution
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Equity Capital Structure, Percentage				52.00%
ICC staff recommended equity capital structure				50.00%
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 117
ICC staff recommended rate increase				$ 110
Pending Rate Case \| Ameren Illinois Company \| Natural gas
Rate And Regulatory Matters [Line Items]
Intervenor recommended return on equity				9.50%
Intervenor recommended equity capital structure				52.00%
Pending Rate Case \| Ameren Illinois Company \| Natural gas \| Subsequent Event
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Return on Equity, Percentage	10.22%
Public Utilities, Requested Equity Capital Structure, Percentage	52.00%
Rate Base	$ 2,900
ICC recommended return on equity percentage	9.89%
ICC staff recommended equity capital structure	50.00%
ICC staff recommended rate base	$ 2,900
Public Utilities, Requested Rate Increase (Decrease), Amount	140
ICC staff recommended rate increase	127
Revenues	$ 77
Intervenor recommended equity capital structure	50.00%
Natural Gas Capital Investments Challenged as Imprudent	$ 53
Challenged Recoveries Under the QIP	$ 3
Pending Rate Case \| Ameren Illinois Company \| Natural gas \| Maximum
Rate And Regulatory Matters [Line Items]
Intervenor recommended rate increase				$ 106
Pending Rate Case \| Ameren Illinois Company \| Natural gas \| Minimum
Rate And Regulatory Matters [Line Items]
Intervenor recommended rate increase				$ 98