Rate And Regulatory Matters (Narrative-Federal) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2020	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Rate And Regulatory Matters [Line Items]
Regulatory liabilities		$ 5,658		$ 5,658		$ 5,848
Revenues		2,306	$ 1,811	5,911	$ 4,849
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Regulatory liabilities		2,532		2,532		$ 2,374
Revenues		904	$ 645	2,697	$ 2,097
Final Rate Order | Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Regulatory liabilities		$ 9		9
Midwest Independent Transmission System Operator, Inc
Rate And Regulatory Matters [Line Items]
Revenues				17
Midwest Independent Transmission System Operator, Inc | Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Revenues				$ 11
Midwest Independent Transmission System Operator, Inc | Final Rate Order
Rate And Regulatory Matters [Line Items]
Approved return on equity percentage	10.02%