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Related Parties (Tables) | 6 Months Ended
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Jun. 30, 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 and six months ended June 30 were as follows (in millions):
| IPL |  | WPL
| Three Months |  | Six Months |  | Three Months |  | Six Months
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Sales credited |  | $1 |  |  |  | $2 |  |  |  | $3 |  |  |  | $4 |  |  |  | $4 |  |  |  | $4 |  |  |  | $7 |  |  |  | $6 |
Purchases billed | 76 |  |  | 78 |  |  | 152 |  |  | 150 |  |  | 14 |  |  | 13 |  |  | 28 |  |  | 37 |
Corporate Services Billings | The amounts billed to IPL and WPL for the three and six months ended June 30 were as follows (in millions):
| IPL |  | WPL
| Three Months |  | Six Months |  | Three Months |  | Six Months
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Corporate Services billings |  | $36 |  |  |  | $34 |  |  |  | $68 |  |  |  | $63 |  |  |  | $23 |  |  |  | $27 |  |  |  | $49 |  |  |  | $50 |
Net Intercompany Payables | Net intercompany payables to Corporate Services were as follows (in millions):
| IPL |  | WPL
| June 30, 2013 |  | December 31, 2012 |  | June 30, 2013 |  | December 31, 2012
Net payables to Corporate Services | $73 |  | $72 |  | $39 |  | $40
Related Amounts Billed Between Parties | The related amounts billed between the parties for the three and six months ended June 30 were as follows (in millions):
| Three Months |  | Six Months
| 2013 |  | 2012 |  | 2013 |  | 2012
ATC billings to WPL |  | $24 |  |  |  | $23 |  |  |  | $48 |  |  |  | $45 |
WPL billings to ATC | 4 |  |  | 2 |  |  | 7 |  |  | 4 |
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 and six months ended June 30 were as follows (in millions):
| IPL |  | WPL
| Three Months |  | Six Months |  | Three Months |  | Six Months
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Sales credited |  | $1 |  |  |  | $2 |  |  |  | $3 |  |  |  | $4 |  |  |  | $4 |  |  |  | $4 |  |  |  | $7 |  |  |  | $6 |
Purchases billed | 76 |  |  | 78 |  |  | 152 |  |  | 150 |  |  | 14 |  |  | 13 |  |  | 28 |  |  | 37 |
Corporate Services Billings | The amounts billed to IPL and WPL for the three and six months ended June 30 were as follows (in millions):
| IPL |  | WPL
| Three Months |  | Six Months |  | Three Months |  | Six Months
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Corporate Services billings |  | $36 |  |  |  | $34 |  |  |  | $68 |  |  |  | $63 |  |  |  | $23 |  |  |  | $27 |  |  |  | $49 |  |  |  | $50 |
Net Intercompany Payables | Net intercompany payables to Corporate Services were as follows (in millions):
| IPL |  | WPL
| June 30, 2013 |  | December 31, 2012 |  | June 30, 2013 |  | December 31, 2012
Net payables to Corporate Services | $73 |  | $72 |  | $39 |  | $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 and six months ended June 30 were as follows (in millions):
| IPL |  | WPL
| Three Months |  | Six Months |  | Three Months |  | Six Months
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Sales credited |  | $1 |  |  |  | $2 |  |  |  | $3 |  |  |  | $4 |  |  |  | $4 |  |  |  | $4 |  |  |  | $7 |  |  |  | $6 |
Purchases billed | 76 |  |  | 78 |  |  | 152 |  |  | 150 |  |  | 14 |  |  | 13 |  |  | 28 |  |  | 37 |
Corporate Services Billings | The amounts billed to IPL and WPL for the three and six months ended June 30 were as follows (in millions):
| IPL |  | WPL
| Three Months |  | Six Months |  | Three Months |  | Six Months
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Corporate Services billings |  | $36 |  |  |  | $34 |  |  |  | $68 |  |  |  | $63 |  |  |  | $23 |  |  |  | $27 |  |  |  | $49 |  |  |  | $50 |
Net Intercompany Payables | Net intercompany payables to Corporate Services were as follows (in millions):
| IPL |  | WPL
| June 30, 2013 |  | December 31, 2012 |  | June 30, 2013 |  | December 31, 2012
Net payables to Corporate Services | $73 |  | $72 |  | $39 |  | $40
Related Amounts Billed Between Parties | The related amounts billed between the parties for the three and six months ended June 30 were as follows (in millions):
| Three Months |  | Six Months
| 2013 |  | 2012 |  | 2013 |  | 2012
ATC billings to WPL |  | $24 |  |  |  | $23 |  |  |  | $48 |  |  |  | $45 |
WPL billings to ATC | 4 |  |  | 2 |  |  | 7 |  |  | 4 |

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