Rate and Regulatory Matters (Narrative-Federal) (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	May 31, 2020	Nov. 30, 2019	Dec. 31, 2021	Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities			$ 5,848	$ 5,282
Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities			$ 2,374	$ 2,063
Midwest Independent Transmission System Operator, Inc
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage			12.38%
Incentive adder to FERC allowed base return on common equity			0.50%
Final Rate Order | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities			$ 9
Final Rate Order | Midwest Independent Transmission System Operator, Inc
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage	10.02%	9.88%	10.32%
Customer Requested Rate on Equity			9.15%
Incentive adder to FERC allowed base return on common equity			0.50%
Final Rate Order | Midwest Independent Transmission System Operator, Inc | Maximum
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage			10.82%