Rate And Regulatory Matters (Narrative-Illinois) (Details) - Ameren Illinois Company $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($)
Rate And Regulatory Matters [Line Items]
Annual investment in energy-efficiency programs	$ 120
Electric Distribution | Minimum
Rate And Regulatory Matters [Line Items]
Return on equity adjustment	0.20%
Electric Distribution | Maximum
Rate And Regulatory Matters [Line Items]
Return on equity adjustment	0.60%
Pending Rate Case | Electric Distribution | IEIMA
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 83
Public Utilities, Requested Equity Capital Structure, Percentage	54.00%
Pending Rate Case | Natural gas
Rate And Regulatory Matters [Line Items]
Natural Gas Capital Investment Prudency Challenge	$ 70
Challenged Recoveries Under the QIP	$ 3