v3.26.1
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, 2026
Dec. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: $ 1,621 $ 1,514
Assets fair value 1,666 1,530
Excluded receivables, payables, and accrued income, net 10 12
Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 1,135 1,028
Assets fair value 1,145 1,028
Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 486 486
Assets fair value 501 489
Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 0 0
Assets fair value 20 13
Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 45 16
Derivative Liability 126 126
Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 10 0
Derivative Liability 26 6
Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 15 3
Derivative Liability 56 51
Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 20 13
Derivative Liability 44 69
Union Electric Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 1,621 1,514
Assets fair value 1,664 1,526
Union Electric Company | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 1,135 1,028
Assets fair value 1,145 1,028
Union Electric Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 486 486
Assets fair value 501 487
Union Electric Company | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 0 0
Assets fair value 18 11
Union Electric Company | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 43 12
Derivative Liability 16 15
Union Electric Company | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 10 0
Derivative Liability 0 5
Union Electric Company | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 15 1
Derivative Liability 15 10
Union Electric Company | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 18 11
Derivative Liability 1 0
Union Electric Company | Fuel oils | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 11 0
Derivative Liability 0 5
Union Electric Company | Fuel oils | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 10 0
Derivative Liability 0 5
Union Electric Company | Fuel oils | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 0
Derivative Liability 0 0
Union Electric Company | Fuel oils | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 1 0
Derivative Liability 0 0
Union Electric Company | Natural gas | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 1
Derivative Liability 15 10
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 0 1
Derivative Liability 14 10
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 32 11
Derivative Liability 1 0
Union Electric Company | Power | 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 | Power | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 15 0
Derivative Liability 1 0
Union Electric Company | Power | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 17 11
Derivative Liability 0 0
Union Electric Company | Equity securities: | U.S. large capitalization    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 1,135 1,028
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: 1,135 1,028
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: 197 225
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: 197 225
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: 184 177
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: 184 177
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: 105 84
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: 105 84
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 2 4
Ameren Illinois Company | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 0 0
Ameren Illinois Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 0 2
Ameren Illinois Company | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 2 2
Ameren Illinois Company | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 110 111
Ameren Illinois Company | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 26 1
Ameren Illinois Company | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 41 41
Ameren Illinois Company | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 43 69
Ameren Illinois Company | Natural gas | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 2 4
Derivative Liability 47 32
Ameren Illinois Company | Natural gas | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 0
Derivative Liability 2 1
Ameren Illinois Company | Natural gas | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 2
Derivative Liability 41 28
Ameren Illinois Company | Natural gas | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 2 2
Derivative Liability 4 3
Ameren Illinois Company | Power | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 63 79
Ameren Illinois Company | Power | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 24 0
Ameren Illinois Company | Power | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 0 13
Ameren Illinois Company | Power | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability $ 39 $ 66