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Asset Retirement Obligations (Tables) | 3 Months Ended
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Mar. 31, 2015
Schedule of Asset Retirement Obligations [Line Items] |
Reconciliation Of Changes In Asset Retirement Obligations | A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2015 |  | 2014 |  | 2015 |  | 2014 |  | 2015 |  | 2014
Balance, January 1 |  | $114.0 |  |  |  | $109.7 |  |  |  | $51.8 |  |  |  | $47.9 |  |  |  | $52.4 |  |  |  | $52.4 |
Liabilities settled | (2.2 | ) |  | (0.5 | ) |  | (2.2 | ) |  | (0.3 | ) |  | — |  |  | (0.2 | )
Liabilities incurred | — |  |  | 16.5 |  |  | — |  |  | 16.3 |  |  | — |  |  | 0.2 |
Accretion expense | 1.0 |  |  | 1.0 |  |  | 0.4 |  |  | 0.5 |  |  | 0.4 |  |  | 0.4 |
Balance, March 31 |  | $112.8 |  |  |  | $126.7 |  |  |  | $50.0 |  |  |  | $64.4 |  |  |  | $52.8 |  |  |  | $52.8 |
Asset Retirement Obligations Expected To Be Recognized [Table Text Block] | Alliant Energy, IPL and WPL currently anticipate recognizing additional AROs in the second quarter of 2015 as a result of the final CCR Rule as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Estimated ARO increase not to exceed | $85 |  | $75 |  | $10
IPL [Member] |
Schedule of Asset Retirement Obligations [Line Items] |
Reconciliation Of Changes In Asset Retirement Obligations | A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2015 |  | 2014 |  | 2015 |  | 2014 |  | 2015 |  | 2014
Balance, January 1 |  | $114.0 |  |  |  | $109.7 |  |  |  | $51.8 |  |  |  | $47.9 |  |  |  | $52.4 |  |  |  | $52.4 |
Liabilities settled | (2.2 | ) |  | (0.5 | ) |  | (2.2 | ) |  | (0.3 | ) |  | — |  |  | (0.2 | )
Liabilities incurred | — |  |  | 16.5 |  |  | — |  |  | 16.3 |  |  | — |  |  | 0.2 |
Accretion expense | 1.0 |  |  | 1.0 |  |  | 0.4 |  |  | 0.5 |  |  | 0.4 |  |  | 0.4 |
Balance, March 31 |  | $112.8 |  |  |  | $126.7 |  |  |  | $50.0 |  |  |  | $64.4 |  |  |  | $52.8 |  |  |  | $52.8 |
Asset Retirement Obligations Expected To Be Recognized [Table Text Block] | Alliant Energy, IPL and WPL currently anticipate recognizing additional AROs in the second quarter of 2015 as a result of the final CCR Rule as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Estimated ARO increase not to exceed | $85 |  | $75 |  | $10
WPL [Member] |
Schedule of Asset Retirement Obligations [Line Items] |
Reconciliation Of Changes In Asset Retirement Obligations | A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2015 |  | 2014 |  | 2015 |  | 2014 |  | 2015 |  | 2014
Balance, January 1 |  | $114.0 |  |  |  | $109.7 |  |  |  | $51.8 |  |  |  | $47.9 |  |  |  | $52.4 |  |  |  | $52.4 |
Liabilities settled | (2.2 | ) |  | (0.5 | ) |  | (2.2 | ) |  | (0.3 | ) |  | — |  |  | (0.2 | )
Liabilities incurred | — |  |  | 16.5 |  |  | — |  |  | 16.3 |  |  | — |  |  | 0.2 |
Accretion expense | 1.0 |  |  | 1.0 |  |  | 0.4 |  |  | 0.5 |  |  | 0.4 |  |  | 0.4 |
Balance, March 31 |  | $112.8 |  |  |  | $126.7 |  |  |  | $50.0 |  |  |  | $64.4 |  |  |  | $52.8 |  |  |  | $52.8 |
Asset Retirement Obligations Expected To Be Recognized [Table Text Block] | Alliant Energy, IPL and WPL currently anticipate recognizing additional AROs in the second quarter of 2015 as a result of the final CCR Rule as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Estimated ARO increase not to exceed | $85 |  | $75 |  | $10

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