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Related Parties (Tables) | 3 Months Ended
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Mar. 31, 2013
Related Party Transaction [Line Items] |
Sales Credited And Purchases Billed | The sales credited to and purchases billed to IPL and WPL for the three months ended March 31 were as follows (in millions):
| IPL |  | WPL
| 2013 |  | 2012 |  | 2013 |  | 2012
Sales credited |  | $2 |  |  |  | $2 |  |  |  | $3 |  |  |  | $2 |
Purchases billed | 76 |  |  | 72 |  |  | 14 |  |  | 24 |
Corporate Services Billings | The amounts billed to IPL and WPL for the three months ended March 31 were as follows (in millions):
| IPL |  | WPL
| 2013 |  | 2012 |  | 2013 |  | 2012
Corporate Services billings |  | $32 |  |  |  | $29 |  |  |  | $26 |  |  |  | $23 |
Net Intercompany Payables | Net intercompany payables to Corporate Services were as follows (in millions):
| IPL |  | WPL
| March 31, 2013 |  | December 31, 2012 |  | March 31, 2013 |  | December 31, 2012
Net payables to Corporate Services | $79 |  | $72 |  | $42 |  | $40
Related Amounts Billed Between Parties | The related amounts billed between the parties for the three months ended March 31 were as follows (in millions):
| 2013 |  | 2012
ATC billings to WPL |  | $24 |  |  |  | $22 |
WPL billings to ATC | 3 |  |  | 2 |
IPL [Member] |
Related Party Transaction [Line Items] |
Sales Credited And Purchases Billed | The sales credited to and purchases billed to IPL and WPL for the three months ended March 31 were as follows (in millions):
| IPL |  | WPL
| 2013 |  | 2012 |  | 2013 |  | 2012
Sales credited |  | $2 |  |  |  | $2 |  |  |  | $3 |  |  |  | $2 |
Purchases billed | 76 |  |  | 72 |  |  | 14 |  |  | 24 |
Corporate Services Billings | The amounts billed to IPL and WPL for the three months ended March 31 were as follows (in millions):
| IPL |  | WPL
| 2013 |  | 2012 |  | 2013 |  | 2012
Corporate Services billings |  | $32 |  |  |  | $29 |  |  |  | $26 |  |  |  | $23 |
Net Intercompany Payables | Net intercompany payables to Corporate Services were as follows (in millions):
| IPL |  | WPL
| March 31, 2013 |  | December 31, 2012 |  | March 31, 2013 |  | December 31, 2012
Net payables to Corporate Services | $79 |  | $72 |  | $42 |  | $40
WPL [Member] |
Related Party Transaction [Line Items] |
Sales Credited And Purchases Billed | The sales credited to and purchases billed to IPL and WPL for the three months ended March 31 were as follows (in millions):
| IPL |  | WPL
| 2013 |  | 2012 |  | 2013 |  | 2012
Sales credited |  | $2 |  |  |  | $2 |  |  |  | $3 |  |  |  | $2 |
Purchases billed | 76 |  |  | 72 |  |  | 14 |  |  | 24 |
Corporate Services Billings | The amounts billed to IPL and WPL for the three months ended March 31 were as follows (in millions):
| IPL |  | WPL
| 2013 |  | 2012 |  | 2013 |  | 2012
Corporate Services billings |  | $32 |  |  |  | $29 |  |  |  | $26 |  |  |  | $23 |
Net Intercompany Payables | Net intercompany payables to Corporate Services were as follows (in millions):
| IPL |  | WPL
| March 31, 2013 |  | December 31, 2012 |  | March 31, 2013 |  | December 31, 2012
Net payables to Corporate Services | $79 |  | $72 |  | $42 |  | $40
Related Amounts Billed Between Parties | The related amounts billed between the parties for the three months ended March 31 were as follows (in millions):
| 2013 |  | 2012
ATC billings to WPL |  | $24 |  |  |  | $22 |
WPL billings to ATC | 3 |  |  | 2 |

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