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Related Parties (Tables) | 9 Months Ended
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Sep. 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 nine months ended September 30 were as follows (in millions):
| IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Sales credited |  | $2 |  |  |  | $3 |  |  |  | $5 |  |  |  | $7 |  |  |  | $3 |  |  |  | $4 |  |  |  | $10 |  |  |  | $10 |
Purchases billed | 108 |  |  | 87 |  |  | 260 |  |  | 237 |  |  | 16 |  |  | 13 |  |  | 44 |  |  | 50 |
Corporate Services Billings | The amounts billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
| IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Corporate Services billings |  | $39 |  |  |  | $34 |  |  |  | $107 |  |  |  | $97 |  |  |  | $28 |  |  |  | $26 |  |  |  | $77 |  |  |  | $76 |
Net Intercompany Payables | Net intercompany payables to Corporate Services were as follows (in millions):
| IPL |  | WPL
| September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012
Net payables to Corporate Services | $95 |  | $72 |  | $46 |  | $40
Related Amounts Billed Between Parties | The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions):
| Three Months |  | Nine Months
| 2013 |  | 2012 |  | 2013 |  | 2012
ATC billings to WPL |  | $24 |  |  |  | $22 |  |  |  | $72 |  |  |  | $67 |
WPL billings to ATC | 2 |  |  | 3 |  |  | 9 |  |  | 7 |
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 nine months ended September 30 were as follows (in millions):
| IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Sales credited |  | $2 |  |  |  | $3 |  |  |  | $5 |  |  |  | $7 |  |  |  | $3 |  |  |  | $4 |  |  |  | $10 |  |  |  | $10 |
Purchases billed | 108 |  |  | 87 |  |  | 260 |  |  | 237 |  |  | 16 |  |  | 13 |  |  | 44 |  |  | 50 |
Corporate Services Billings | The amounts billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
| IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Corporate Services billings |  | $39 |  |  |  | $34 |  |  |  | $107 |  |  |  | $97 |  |  |  | $28 |  |  |  | $26 |  |  |  | $77 |  |  |  | $76 |
Net Intercompany Payables | Net intercompany payables to Corporate Services were as follows (in millions):
| IPL |  | WPL
| September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012
Net payables to Corporate Services | $95 |  | $72 |  | $46 |  | $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 nine months ended September 30 were as follows (in millions):
| IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Sales credited |  | $2 |  |  |  | $3 |  |  |  | $5 |  |  |  | $7 |  |  |  | $3 |  |  |  | $4 |  |  |  | $10 |  |  |  | $10 |
Purchases billed | 108 |  |  | 87 |  |  | 260 |  |  | 237 |  |  | 16 |  |  | 13 |  |  | 44 |  |  | 50 |
Corporate Services Billings | The amounts billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
| IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Corporate Services billings |  | $39 |  |  |  | $34 |  |  |  | $107 |  |  |  | $97 |  |  |  | $28 |  |  |  | $26 |  |  |  | $77 |  |  |  | $76 |
Net Intercompany Payables | Net intercompany payables to Corporate Services were as follows (in millions):
| IPL |  | WPL
| September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012
Net payables to Corporate Services | $95 |  | $72 |  | $46 |  | $40
Related Amounts Billed Between Parties | The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions):
| Three Months |  | Nine Months
| 2013 |  | 2012 |  | 2013 |  | 2012
ATC billings to WPL |  | $24 |  |  |  | $22 |  |  |  | $72 |  |  |  | $67 |
WPL billings to ATC | 2 |  |  | 3 |  |  | 9 |  |  | 7 |

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