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Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Commodity Contracts [Member]        
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance $ 56 $ 51 $ 25 $ 24
Total net gains (losses) included in changes in net assets (realized/unrealized) (2) 2 5 (7)
Purchases     50 59
Sales (2) 0 (2) (1)
Settlements (13) (16) (39) (38)
Ending balance 39 37 39 37
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 (4) 2 4 (7)
Commodity Contracts [Member] | IPL [Member]        
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance 44 40 20 19
Total net gains (losses) included in changes in net assets (realized/unrealized) (5) 0 1 (7)
Purchases     40 45
Sales (1) 0 (1) (1)
Settlements (8) (11) (30) (27)
Ending balance 30 29 30 29
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 (6) 0 1 (7)
Commodity Contracts [Member] | WPL [Member]        
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance 12 11 5 5
Total net gains (losses) included in changes in net assets (realized/unrealized) 3 2 4 0
Purchases     10 14
Sales (1) 0 (1) 0
Settlements (5) (5) (9) (11)
Ending balance 9 8 9 8
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 2 2 3 0
Deferred Proceeds [Member]        
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance 235 171 163 216
Total net gains (losses) included in changes in net assets (realized/unrealized) 0 0 0 0
Purchases     0 0
Sales 0 0 0 0
Settlements (4) 41 68 (4)
Ending balance 231 212 231 212
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 0 0 0 0
Deferred Proceeds [Member] | IPL [Member]        
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance 235 171 163 216
Total net gains (losses) included in changes in net assets (realized/unrealized) 0 0 0 0
Purchases     0 0
Sales 0 0 0 0
Settlements (4) 41 68 (4)
Ending balance 231 212 231 212
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $ 0 $ 0 $ 0 $ 0