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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, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	$ 216	$ 155	$ 301	$ 176
Short-term debt	1,070	545
Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	13	8	145	39
Short-term debt	329	165
Debt Issuance Costs, Net	41	38
Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	191	133	$ 147	$ 125
Short-term debt	264	103
Debt Issuance Costs, Net	44	39
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	216	155
Investments in industrial development revenue bonds	240	248
Short-term debt	1,070	545
Long-term debt (including current portion)	14,025	13,067
Debt Issuance Costs, Net	99	94
Carrying Amount \| Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	13	8
Investments in industrial development revenue bonds	240	248
Short-term debt	329	165
Long-term debt (including current portion)	6,086	5,619
Debt Issuance Costs, Net	41	38
Carrying Amount \| Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	191	133
Short-term debt	264	103
Long-term debt (including current portion)	4,835	4,392
Debt Issuance Costs, Net	44	39
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	216	155
Investments, Fair Value Disclosure	240	248
Short-term Debt, Fair Value	1,070	545
Long-term Debt, Fair Value	12,453	14,521
Fair Value \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	216	155
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Fair Value \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	0	0
Investments, Fair Value Disclosure	240	248
Short-term Debt, Fair Value	1,070	545
Long-term Debt, Fair Value	11,989	13,930
Fair Value \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	0	0
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	464	591
Fair Value \| Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	13	8
Investments, Fair Value Disclosure	240	248
Short-term Debt, Fair Value	329	165
Long-term Debt, Fair Value	5,365	6,321
Fair Value \| Union Electric Company \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	13	8
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Fair Value \| Union Electric Company \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	0	0
Investments, Fair Value Disclosure	240	248
Short-term Debt, Fair Value	329	165
Long-term Debt, Fair Value	5,365	6,321
Fair Value \| Union Electric Company \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	0	0
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Fair Value \| Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	191	133
Short-term Debt, Fair Value	264	103
Long-term Debt, Fair Value	4,320	4,971
Fair Value \| Ameren Illinois Company \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	191	133
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Fair Value \| Ameren Illinois Company \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	0	0
Short-term Debt, Fair Value	264	103
Long-term Debt, Fair Value	4,320	4,971
Fair Value \| Ameren Illinois Company \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	$ 0	$ 0