Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Basis Of Presentation And Significant Accounting Policies [Line Items]
Unconsolidated variable interest	$ 92	$ 64
Cash Surrender Value of Life Insurance	225	219
Corporate owned life insurance, borrowings	124	117
Ameren Illinois Company
Basis Of Presentation And Significant Accounting Policies [Line Items]
Cash Surrender Value of Life Insurance	132	126
Corporate owned life insurance, borrowings	124	$ 117
Partnership Funding Commitment
Basis Of Presentation And Significant Accounting Policies [Line Items]
Outstanding funding commitments	$ 25

Basis Of Presentation And Significant Accounting Policies [Line Items]

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- Definition

Corporate Owned Life Insurance, Borrowings

+ References

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Carrying amount as of the balance sheet date of amounts which could be received based on the terms of the insurance contract upon surrendering life policies owned by the entity.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(17))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480657/210-10-S50-7

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Portion of equity (net assets) in a variable interest entity (VIE) not attributable, directly or indirectly, to the parent entity. That is, this is the portion of equity in a VIE that is attributable to the noncontrolling interest (previously referred to as minority interest).

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Amount of unrecorded obligation to transfer funds in future for fixed or minimum amount or quantity of product and service at fixed or minimum price. Includes, but is not limited to, lease not yet commenced and take-or-pay and throughput contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 440
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482648/440-10-50-4

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-3

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