Rate And Regulatory Matters (Narrative-Federal) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	May 31, 2020	Mar. 31, 2023	Mar. 31, 2022
Rate And Regulatory Matters [Line Items]
ROE Change		0.50%
Revenues		$ 2,062	$ 1,879
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Revenues		1,101	$ 1,024
Midwest Independent Transmission System Operator, Inc
Rate And Regulatory Matters [Line Items]
Revenues		19
Midwest Independent Transmission System Operator, Inc | Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Revenues		$ 13
Midwest Independent Transmission System Operator, Inc | Final Rate Order
Rate And Regulatory Matters [Line Items]
Approved return on equity percentage	10.02%