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Asset Retirement Obligations
 6 Months Ended
Jun. 30, 2016
Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations
ASSET RETIREMENT OBLIGATIONS
A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
 
Alliant Energy
 
IPL
 
WPL
 
2016
 
2015
 
2016
 
2015
 
2016
 
2015
Balance, January 1

$214.0

 

$114.0

 

$132.9

 

$51.8

 

$71.9

 

$52.4

Revisions in estimated cash flows (a)
3.9

 
2.1

 
4.2

 
0.9

 
(0.3
)
 
1.2

Liabilities settled
(7.3
)
 
(6.4
)
 
(2.0
)
 
(2.4
)
 
(5.3
)
 
(4.0
)
Liabilities incurred (a)
2.2

 
72.3

 
0.7

 
56.1

 
1.5

 
16.2

Accretion expense
3.2

 
2.2

 
1.9

 
0.9

 
1.1

 
0.9

Balance, June 30

$216.0

 

$184.2

 

$137.7

 

$107.3

 

$68.9

 

$66.7



(a)
In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and was effective October 2015. IPL and WPL have nine and three coal-fired EGUs, respectively, with coal ash ponds that are impacted by this rule. In addition, IPL and WPL have four and two active CCR landfills, respectively, that are impacted by this rule. In the second quarter of 2015, Alliant Energy, IPL and WPL recognized additional AROs of $74 million, $57 million and $17 million, respectively, as a result of the final CCR Rule. The increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.
IPL [Member]  
Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations
ASSET RETIREMENT OBLIGATIONS
A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
 
Alliant Energy
 
IPL
 
WPL
 
2016
 
2015
 
2016
 
2015
 
2016
 
2015
Balance, January 1

$214.0

 

$114.0

 

$132.9

 

$51.8

 

$71.9

 

$52.4

Revisions in estimated cash flows (a)
3.9

 
2.1

 
4.2

 
0.9

 
(0.3
)
 
1.2

Liabilities settled
(7.3
)
 
(6.4
)
 
(2.0
)
 
(2.4
)
 
(5.3
)
 
(4.0
)
Liabilities incurred (a)
2.2

 
72.3

 
0.7

 
56.1

 
1.5

 
16.2

Accretion expense
3.2

 
2.2

 
1.9

 
0.9

 
1.1

 
0.9

Balance, June 30

$216.0

 

$184.2

 

$137.7

 

$107.3

 

$68.9

 

$66.7



(a)
In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and was effective October 2015. IPL and WPL have nine and three coal-fired EGUs, respectively, with coal ash ponds that are impacted by this rule. In addition, IPL and WPL have four and two active CCR landfills, respectively, that are impacted by this rule. In the second quarter of 2015, Alliant Energy, IPL and WPL recognized additional AROs of $74 million, $57 million and $17 million, respectively, as a result of the final CCR Rule. The increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.
WPL [Member]  
Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations
ASSET RETIREMENT OBLIGATIONS
A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
 
Alliant Energy
 
IPL
 
WPL
 
2016
 
2015
 
2016
 
2015
 
2016
 
2015
Balance, January 1

$214.0

 

$114.0

 

$132.9

 

$51.8

 

$71.9

 

$52.4

Revisions in estimated cash flows (a)
3.9

 
2.1

 
4.2

 
0.9

 
(0.3
)
 
1.2

Liabilities settled
(7.3
)
 
(6.4
)
 
(2.0
)
 
(2.4
)
 
(5.3
)
 
(4.0
)
Liabilities incurred (a)
2.2

 
72.3

 
0.7

 
56.1

 
1.5

 
16.2

Accretion expense
3.2

 
2.2

 
1.9

 
0.9

 
1.1

 
0.9

Balance, June 30

$216.0

 

$184.2

 

$137.7

 

$107.3

 

$68.9

 

$66.7



(a)
In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and was effective October 2015. IPL and WPL have nine and three coal-fired EGUs, respectively, with coal ash ponds that are impacted by this rule. In addition, IPL and WPL have four and two active CCR landfills, respectively, that are impacted by this rule. In the second quarter of 2015, Alliant Energy, IPL and WPL recognized additional AROs of $74 million, $57 million and $17 million, respectively, as a result of the final CCR Rule. The increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.