Annual investment in energy-efficiency programs.

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ICC Staff's recommended capital structure

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ICC Staff's recommended ROE

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ICC Staff's recommended rate base

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The rate increase recommended by the ICC staff.

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Illinois Attorney General's office's recommended capital structure

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Illinois Attorney General's office's recommended ROE

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Illinois Attorney General's office's recommended rate base

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Illinois Attorney General's office's recommended rate increase

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

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

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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 return on equity.

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Rate And Regulatory Matters (Narrative-Illinois) (Details) - Ameren Illinois Company - USD ($) $ in Millions	3 Months Ended					6 Months Ended
	Mar. 31, 2028	Mar. 31, 2027	Mar. 31, 2026	Sep. 30, 2025	Mar. 31, 2025	Jun. 30, 2025
Rate And Regulatory Matters [Line Items]
Annual investment in energy-efficiency programs						$ 126
IETL \| 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 \| 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 \| Electric Distribution \| Subsequent Event
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 60
Public Utilities, Requested Equity Capital Structure, Percentage				50.00%
ICC Staff's recommended rate base				$ 49
Pending Rate Case \| Electric Energy-Efficiency
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount						$ 12
Pending Rate Case \| Natural gas \| Subsequent Event
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 135
Public Utilities, Requested Equity Capital Structure, Percentage				52.00%
Public Utilities, Requested Return on Equity, Percentage				10.70%
Rate Base				$ 3,300
ICC staff recommended rate increase				$ 103
ICC recommended ROE				9.93%
ICC Staff's recommended capital structure				50.00%
ICC Staff's recommended rate base				$ 3,200
Illinois Attorney General's office's recommended rate increase				$ 55
Illinois Attorney General's office's recommended ROE				9.45%
Illinois Attorney General's office's recommended capital structure				50.00%
Illinois Attorney General's office's recommended rate base				$ 3,000