Supplemental Information (Schedule of Asset Retirement Obligations) (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2026	Dec. 31, 2025
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	$ 854
Liabilities incurred	7
Liabilities settled	3
Accretion	28
Change in estimates	(20)
Asset Retirement Obligation, Ending Balance	866
Other current liabilities	469	$ 504
Union Electric Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	849
Liabilities incurred	7
Liabilities settled	3
Accretion	28
Change in estimates	(20)
Asset Retirement Obligation, Ending Balance	861
Other current liabilities	193	178
Ameren Illinois Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	5
Liabilities incurred	0
Liabilities settled	1
Accretion	1
Change in estimates	0
Asset Retirement Obligation, Ending Balance	5
Other current liabilities	126	135
Balance Sheet Location [Axis]: us-gaap:OtherLiabilitiesCurrent
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Current asset retirement obligations	$ 3	$ 5

[Line Items] for Asset Retirement Obligation [Table]

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The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

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Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

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Current portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

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Amount of asset retirement obligations incurred during the period.

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Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

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Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

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Amount of liabilities classified as other, due within one year or the normal operating cycle, if longer.

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