Commitments And Contingencies (Environmental Matters) (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2023 USD ($) scrubber site	Dec. 31, 2022 USD ($)
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 798	$ 786
Minimum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	90
Maximum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	$ 120
Union Electric Company
Loss Contingencies [Line Items]
Number of Energy Center Scrubbers | scrubber	2
Asset Retirement Obligation	$ 794	782
Union Electric Company | Coal Fired Electric Generation Equipment
Loss Contingencies [Line Items]
Plant To Be Abandoned, Net	550
Union Electric Company | Minimum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	90
Union Electric Company | Maximum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	120
Ameren Illinois Company
Loss Contingencies [Line Items]
Asset Retirement Obligation	4	$ 4
Manufactured Gas Plant
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 61
Manufactured Gas Plant | Ameren Illinois Company
Loss Contingencies [Line Items]
Number of remediation sites | site	44
Accrual for environmental loss contingencies	$ 61
Manufactured Gas Plant | Ameren Illinois Company | Minimum
Loss Contingencies [Line Items]
Estimate of possible loss	61
Manufactured Gas Plant | Ameren Illinois Company | Maximum
Loss Contingencies [Line Items]
Estimate of possible loss	112
Rush Island Energy Center | Union Electric Company
Loss Contingencies [Line Items]
Rate Base	500
New CCR Rules Estimate
Loss Contingencies [Line Items]
Asset Retirement Obligation	45
New CCR Rules Estimate | Union Electric Company
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 45