v3.25.2
Fair Value Measurements (Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - USD ($)
$ in Millions
Jun. 30, 2025
Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: $ 1,406 $ 1,333
Assets fair value 1,435 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: 967 911
Assets fair value 968 911
Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 439 422
Assets fair value 449 429
Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 0 0
Assets fair value 18 9
Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 29 16
Derivative Liability 113 103
Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 1 0
Derivative Liability 4 5
Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 10 7
Derivative Liability 28 39
Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 18 9
Derivative Liability 81 59
Union Electric Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 1,406 1,333
Assets fair value 1,423 1,343
Union Electric Company | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 967 911
Assets fair value 967 911
Union Electric Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 439 422
Assets fair value 443 426
Union Electric Company | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 0 0
Assets fair value 13 6
Union Electric Company | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 17 10
Derivative Liability 13 15
Union Electric Company | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 0
Derivative Liability 4 4
Union Electric Company | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 4 4
Derivative Liability 8 11
Union Electric Company | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 13 6
Derivative Liability 1 0
Union Electric Company | Fuel oils | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 4 4
Union Electric Company | Fuel oils | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 4 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 4 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 4 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 0 0
Derivative Liability 1 0
Union Electric Company | Power | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 13 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 13 6
Union Electric Company | Equity securities: | U.S. large capitalization    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 967 911
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: 967 911
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: 179 191
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: 179 191
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: 163 145
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: 163 145
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: 97 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: 97 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 12 6
Ameren Illinois Company | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 1 0
Ameren Illinois Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 6 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 100 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 20 28
Ameren Illinois Company | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 80 59
Ameren Illinois Company | Natural gas | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 12 6
Derivative Liability 24 35
Ameren Illinois Company | Natural gas | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 1 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 6 3
Derivative Liability 20 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 4 6
Ameren Illinois Company | Power | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 76 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 $ 76 $ 53