Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Financial Assets and Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 272	$ 216	$ 155	$ 301
Short-term debt	536	1,070
Ameren Missouri
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	10	13	8	145
Short-term debt	170	329
Debt Issuance Costs, Net	45	41
Ameren Missouri \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	170	329
Ameren Missouri \| Related Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	306	0
Ameren Illinois
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	234	191	$ 133	$ 147
Short-term debt	366	264
Debt Issuance Costs, Net	47	44
Ameren Illinois \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	366	264
Ameren Illinois \| Related Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	135	0
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	272	216
Long-term debt (including current portion)	15,970	14,025
Investments in industrial development revenue bonds		240
Debt Issuance Costs, Net	111	99
Carrying Amount \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	536	1,070
Carrying Amount \| Ameren Missouri
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	10	13
Long-term debt (including current portion)	6,341	6,086
Investments in industrial development revenue bonds		240
Debt Issuance Costs, Net	45	41
Carrying Amount \| Ameren Missouri \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	170	329
Carrying Amount \| Ameren Missouri \| Related Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	306
Carrying Amount \| Ameren Illinois
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	234	191
Long-term debt (including current portion)	5,232	4,835
Debt Issuance Costs, Net	47	44
Carrying Amount \| Ameren Illinois \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	366	264
Carrying Amount \| Ameren Illinois \| Related Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	135
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	272	216
Long-term Debt, Fair Value	14,833	12,453
Investments, Fair Value Disclosure		240
Fair Value \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	536	1,070
Fair Value \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	272	216
Long-term Debt, Fair Value	0	0
Investments, Fair Value Disclosure		0
Fair Value \| Level 1 \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0	0
Fair Value \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Long-term Debt, Fair Value	14,366	11,989
Investments, Fair Value Disclosure		240
Fair Value \| Level 2 \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	536	1,070
Fair Value \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Long-term Debt, Fair Value	467	464
Investments, Fair Value Disclosure		0
Fair Value \| Level 3 \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0	0
Fair Value \| Ameren Missouri
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	10	13
Long-term Debt, Fair Value	5,800	5,365
Investments, Fair Value Disclosure		240
Fair Value \| Ameren Missouri \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	170	329
Fair Value \| Ameren Missouri \| Related Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	306
Fair Value \| Ameren Missouri \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	10	13
Long-term Debt, Fair Value	0	0
Investments, Fair Value Disclosure		0
Fair Value \| Ameren Missouri \| Level 1 \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0	0
Fair Value \| Ameren Missouri \| Level 1 \| Related Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0
Fair Value \| Ameren Missouri \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Long-term Debt, Fair Value	5,800	5,365
Investments, Fair Value Disclosure		240
Fair Value \| Ameren Missouri \| Level 2 \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	170	329
Fair Value \| Ameren Missouri \| Level 2 \| Related Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	306
Fair Value \| Ameren Missouri \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Long-term Debt, Fair Value	0	0
Investments, Fair Value Disclosure		0
Fair Value \| Ameren Missouri \| Level 3 \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0	0
Fair Value \| Ameren Missouri \| Level 3 \| Related Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0
Fair Value \| Ameren Illinois
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	234	191
Long-term Debt, Fair Value	4,867	4,320
Fair Value \| Ameren Illinois \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	366	264
Fair Value \| Ameren Illinois \| Related Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	135
Fair Value \| Ameren Illinois \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	234	191
Long-term Debt, Fair Value	0	0
Fair Value \| Ameren Illinois \| Level 1 \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0	0
Fair Value \| Ameren Illinois \| Level 1 \| Related Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0
Fair Value \| Ameren Illinois \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Long-term Debt, Fair Value	4,867	4,320
Fair Value \| Ameren Illinois \| Level 2 \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	366	264
Fair Value \| Ameren Illinois \| Level 2 \| Related Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	135
Fair Value \| Ameren Illinois \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Long-term Debt, Fair Value	0	0
Fair Value \| Ameren Illinois \| Level 3 \| Nonrelated Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0	$ 0
Fair Value \| Ameren Illinois \| Level 3 \| Related Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	$ 0