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Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Short-term Debt [Line Items]
Average daily amount outstanding	$ 1,012	$ 620
Weighted-average interest rate	4.59%	5.53%
Short-term Debt, Maximum Amount Outstanding During Period	$ 1,603	$ 1,542
Peak interest rate	4.75%	5.68%
Parent Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 637	$ 177
Weighted-average interest rate	4.60%	5.46%
Short-term Debt, Maximum Amount Outstanding During Period	$ 1,139	$ 948
Peak interest rate	4.75%	5.60%
Union Electric Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 245	$ 187
Weighted-average interest rate	4.58%	5.52%
Short-term Debt, Maximum Amount Outstanding During Period	$ 650	$ 576
Peak interest rate	4.72%	5.68%
Ameren Illinois Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 130	$ 256
Weighted-average interest rate	4.55%	5.57%
Short-term Debt, Maximum Amount Outstanding During Period	$ 425	$ 694
Peak interest rate	4.70%	5.68%

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Weighted average interest rate of short-term debt outstanding calculated at point in time.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481544/470-10-50-7

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(b))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

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- Definition

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1402
-Paragraph a
-Publisher SEC

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1402
-Paragraph b
-Subparagraph (1)
-Publisher SEC

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(3))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

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For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, the maximum amount borrowed at any time during the period.

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