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Commitments And Contingencies (Narrative) (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2017
USD ($)
Long-term Purchase Commitment [Line Items]  
Minimum future commitments $ 2,410
Present value abandonment obligation 33
Purchased Power [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments 1,232 [1]
Capital Purchase Obligation [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments 82
IPL [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments 1,669
Maximum indemnification limit 17
IPL [Member] | Purchased Power [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments 1,159 [1]
IPL [Member] | Capital Purchase Obligation [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments 15
WPL [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments 735
WPL [Member] | Purchased Power [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments 73 [1]
WPL [Member] | Capital Purchase Obligation [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments 67
Indemnification Agreement [Member]  
Long-term Purchase Commitment [Line Items]  
Maximum indemnification limit 98
Indemnification Agreement [Member] | Purchased Power [Member]  
Long-term Purchase Commitment [Line Items]  
Maximum indemnification limit $ 17
[1] Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.