Commitments And Contingencies (Environmental Matters) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2025 USD ($) energyCenter scrubber site	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Other current liabilities	$ 570	$ 475
Other deferred credits and liabilities	540	487
Other operations and maintenance	1,974	1,969	$ 1,866
Asset Retirement Obligation	$ 854	827	791
Environmental Loss Contingency Statement Of Financial Position Extensible Enumeration Not Disclosed Flag	false
Rush Island Energy Center Additional Mitigation Relief Ordered
Other current liabilities	$ 36	40
Other deferred credits and liabilities		24
Other operations and maintenance		59
Ameren Missouri
Number of Energy Center Scrubbers \| scrubber	2
Other current liabilities	$ 212	235
Other deferred credits and liabilities	184	150
Other operations and maintenance	1,029	1,050	1,003
Asset Retirement Obligation	$ 849	823	787
Number of Ameren Missouri Natural Gas Energy Centers Subject To IETL \| energyCenter	4
Ameren Missouri \| Rush Island Energy Center Additional Mitigation Relief Ordered
Other current liabilities	$ 36	40
Other deferred credits and liabilities		24
Other operations and maintenance		59
Ameren Illinois
Other current liabilities	227	172
Other deferred credits and liabilities	268	273
Other operations and maintenance	945	906	818
Asset Retirement Obligation	$ 5	$ 4	$ 4
Number of remediation sites \| site	3
Manufactured Gas Plant
Accrual for environmental loss contingencies	$ 45
Manufactured Gas Plant \| Ameren Illinois
Number of remediation sites \| site	44
Accrual for environmental loss contingencies	$ 45
Minimum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	70
Minimum \| Ameren Missouri
Estimated capital costs to comply with existing and known federal and state air emissions regulations	70
Minimum \| Manufactured Gas Plant \| Ameren Illinois
Estimate of possible loss	45
Maximum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	100
Maximum \| Ameren Missouri
Estimated capital costs to comply with existing and known federal and state air emissions regulations	100
Maximum \| Manufactured Gas Plant \| Ameren Illinois
Estimate of possible loss	90
New CCR Rules Estimate
Asset Retirement Obligation	56
New CCR Rules Estimate \| Ameren Missouri
Asset Retirement Obligation	$ 56

AMEREN CORP 10-K