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Asset Retirement Obligations (Tables)
 6 Months Ended
Jun. 30, 2014
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
 
2014
 
2013
 
2014
 
2013
 
2014
 
2013
Balance, January 1

$109.7

 

$101.5

 

$47.9

 

$45.5

 

$52.4

 

$46.9

Revisions in estimated cash flows
—

 
3.4

 
—

 
0.8

 
—

 
2.6

Liabilities settled
(0.7
)
 
(0.1
)
 
(0.4
)
 
—

 
(0.3
)
 
(0.1
)
Liabilities incurred (a)
16.5

 
—

 
16.3

 
—

 
0.2

 
—

Accretion expense
2.1

 
1.8

 
1.0

 
0.8

 
0.8

 
0.8

Balance, June 30

$127.6

 

$106.6

 

$64.8

 

$47.1

 

$53.1

 

$50.2



(a)
In 2014, IPL recorded AROs of $12.0 million related to its Sutherland Generating Station.
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
 
2014
 
2013
 
2014
 
2013
 
2014
 
2013
Balance, January 1

$109.7

 

$101.5

 

$47.9

 

$45.5

 

$52.4

 

$46.9

Revisions in estimated cash flows
—

 
3.4

 
—

 
0.8

 
—

 
2.6

Liabilities settled
(0.7
)
 
(0.1
)
 
(0.4
)
 
—

 
(0.3
)
 
(0.1
)
Liabilities incurred (a)
16.5

 
—

 
16.3

 
—

 
0.2

 
—

Accretion expense
2.1

 
1.8

 
1.0

 
0.8

 
0.8

 
0.8

Balance, June 30

$127.6

 

$106.6

 

$64.8

 

$47.1

 

$53.1

 

$50.2



(a)
In 2014, IPL recorded AROs of $12.0 million related to its Sutherland Generating Station.
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
 
2014
 
2013
 
2014
 
2013
 
2014
 
2013
Balance, January 1

$109.7

 

$101.5

 

$47.9

 

$45.5

 

$52.4

 

$46.9

Revisions in estimated cash flows
—

 
3.4

 
—

 
0.8

 
—

 
2.6

Liabilities settled
(0.7
)
 
(0.1
)
 
(0.4
)
 
—

 
(0.3
)
 
(0.1
)
Liabilities incurred (a)
16.5

 
—

 
16.3

 
—

 
0.2

 
—

Accretion expense
2.1

 
1.8

 
1.0

 
0.8

 
0.8

 
0.8

Balance, June 30

$127.6

 

$106.6

 

$64.8

 

$47.1

 

$53.1

 

$50.2



(a)
In 2014, IPL recorded AROs of $12.0 million related to its Sutherland Generating Station.