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Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Financial Assets and Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	$ 237	$ 216	$ 154	$ 155
Short-term debt	1,248	1,070
Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	11	13	9	8
Short-term debt	197	329
Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	217	191	$ 137	$ 133
Short-term debt	324	264
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	237	216
Investments in industrial development revenue bonds		240
Short-term debt	1,248	1,070
Long-term debt (including current portion)	14,281	14,025
Debt Issuance Costs, Net	103	99
Carrying Amount \| Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	11	13
Investments in industrial development revenue bonds		240
Short-term debt	197	329
Long-term debt (including current portion)	6,341	6,086
Debt Issuance Costs, Net	45	41
Carrying Amount \| Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	217	191
Short-term debt	324	264
Long-term debt (including current portion)	4,836	4,835
Debt Issuance Costs, Net	44	44
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	237	216
Investments, Fair Value Disclosure		240
Short-term Debt, Fair Value	1,248	1,070
Long-term Debt, Fair Value	12,881	12,453
Fair Value \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	237	216
Investments, Fair Value Disclosure		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]
Cash, cash equivalents, and restricted cash	0	0
Investments, Fair Value Disclosure		240
Short-term Debt, Fair Value	1,248	1,070
Long-term Debt, Fair Value	12,408	11,989
Fair Value \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Investments, Fair Value Disclosure		0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	473	464
Fair Value \| Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	11	13
Investments, Fair Value Disclosure		240
Short-term Debt, Fair Value	197	329
Long-term Debt, Fair Value	5,706	5,365
Fair Value \| Union Electric Company \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	11	13
Investments, Fair Value Disclosure		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]
Cash, cash equivalents, and restricted cash	0	0
Investments, Fair Value Disclosure		240
Short-term Debt, Fair Value	197	329
Long-term Debt, Fair Value	5,706	5,365
Fair Value \| Union Electric Company \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Investments, Fair Value Disclosure		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]
Cash, cash equivalents, and restricted cash	217	191
Short-term Debt, Fair Value	324	264
Long-term Debt, Fair Value	4,368	4,320
Fair Value \| Ameren Illinois Company \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	217	191
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]
Cash, cash equivalents, and restricted cash	0	0
Short-term Debt, Fair Value	324	264
Long-term Debt, Fair Value	4,368	4,320
Fair Value \| Ameren Illinois Company \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	$ 0	$ 0