Fair Value Measurements (Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	$ 1,304	$ 1,333
Assets fair value	1,331	1,349
Excluded receivables, payables, and accrued income, net	8	9
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	868	911
Assets fair value	870	911
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	436	422
Assets fair value	450	429
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Assets fair value	11	9
Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	27	16
Derivative Liability	99	103
Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	2	0
Derivative Liability	3	5
Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	14	7
Derivative Liability	25	39
Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	11	9
Derivative Liability	71	59
Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	1,304	1,333
Assets fair value	1,315	1,343
Union Electric Company | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	868	911
Assets fair value	868	911
Union Electric Company | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	436	422
Assets fair value	441	426
Union Electric Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Assets fair value	6	6
Union Electric Company | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	11	10
Derivative Liability	12	15
Union Electric Company | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Derivative Liability	3	4
Union Electric Company | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	5	4
Derivative Liability	8	11
Union Electric Company | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	6	6
Derivative Liability	1	0
Union Electric Company | Fuel oils | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	3	4
Union Electric Company | Fuel oils | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	3	4
Union Electric Company | Fuel oils | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0	0
Union Electric Company | Fuel oils | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0	0
Union Electric Company | Natural gas | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	6	4
Derivative Liability	9	11
Union Electric Company | Natural gas | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Derivative Liability	0	0
Union Electric Company | Natural gas | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	5	4
Derivative Liability	8	11
Union Electric Company | Natural gas | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	1	0
Derivative Liability	1	0
Union Electric Company | Power | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	5	6
Union Electric Company | Power | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Union Electric Company | Power | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Union Electric Company | Power | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	5	6
Union Electric Company | Equity securities: | U.S. large capitalization
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	868	911
Union Electric Company | Equity securities: | U.S. large capitalization | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	868	911
Union Electric Company | Equity securities: | U.S. large capitalization | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company | Equity securities: | U.S. large capitalization | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company | Debt securities: | U.S. Treasury and agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	188	191
Union Electric Company | Debt securities: | U.S. Treasury and agency securities | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company | Debt securities: | U.S. Treasury and agency securities | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	188	191
Union Electric Company | Debt securities: | U.S. Treasury and agency securities | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company | Debt securities: | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	156	145
Union Electric Company | Debt securities: | Corporate bonds | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company | Debt securities: | Corporate bonds | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	156	145
Union Electric Company | Debt securities: | Corporate bonds | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company | Debt securities: | Other Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	92	86
Union Electric Company | Debt securities: | Other Debt Securities | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company | Debt securities: | Other Debt Securities | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	92	86
Union Electric Company | Debt securities: | Other Debt Securities | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	16	6
Ameren Illinois Company | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	2	0
Ameren Illinois Company | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	9	3
Ameren Illinois Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	5	3
Ameren Illinois Company | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	87	88
Ameren Illinois Company | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0	1
Ameren Illinois Company | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	17	28
Ameren Illinois Company | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	70	59
Ameren Illinois Company | Natural gas | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	16	6
Derivative Liability	20	35
Ameren Illinois Company | Natural gas | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	2	0
Derivative Liability	0	1
Ameren Illinois Company | Natural gas | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	9	3
Derivative Liability	17	28
Ameren Illinois Company | Natural gas | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	5	3
Derivative Liability	3	6
Ameren Illinois Company | Power | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	67	53
Ameren Illinois Company | Power | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0	0
Ameren Illinois Company | Power | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0	0
Ameren Illinois Company | Power | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	$ 67	$ 53