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Asset Retirement Obligations
 12 Months Ended
Dec. 31, 2018
Schedule of Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations (AROs)
ASSET RETIREMENT OBLIGATIONS
Recognized AROs relate to legal obligations for the removal, closure or dismantlement of several assets including, but not limited to, wind farms, ash ponds, active ash landfills, solar generation and above ground storage tanks. Recognized AROs also include legal obligations for the management and final disposition of asbestos and polychlorinated biphenyls. AROs are recorded in “Other current liabilities” and “Other liabilities” on the balance sheets. Refer to Note 2 for information regarding regulatory assets related to AROs. A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
 
Alliant Energy
 
IPL
 
WPL
 
2018
 
2017
 
2018
 
2017
 
2018
 
2017
Balance, January 1

$184.5

 

$195.7

 

$134.1

 

$124.7

 

$50.4

 

$61.4

Revisions in estimated cash flows
(10.1
)
 
4.3

 
(10.1
)
 
7.0

 
—

 
(2.7
)
Liabilities settled
(10.4
)
 
(23.5
)
 
(9.7
)
 
(13.1
)
 
(0.7
)
 
(10.4
)
Liabilities incurred
7.3

 
2.0

 
—

 
11.7

 
7.3

 
—

Accretion expense
6.2

 
6.0

 
4.0

 
3.8

 
2.2

 
2.1

Balance, December 31

$177.5

 

$184.5

 

$118.3

 

$134.1

 

$59.2

 

$50.4
IPL [Member]  
Schedule of Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations (AROs)
ASSET RETIREMENT OBLIGATIONS
Recognized AROs relate to legal obligations for the removal, closure or dismantlement of several assets including, but not limited to, wind farms, ash ponds, active ash landfills, solar generation and above ground storage tanks. Recognized AROs also include legal obligations for the management and final disposition of asbestos and polychlorinated biphenyls. AROs are recorded in “Other current liabilities” and “Other liabilities” on the balance sheets. Refer to Note 2 for information regarding regulatory assets related to AROs. A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
 
Alliant Energy
 
IPL
 
WPL
 
2018
 
2017
 
2018
 
2017
 
2018
 
2017
Balance, January 1

$184.5

 

$195.7

 

$134.1

 

$124.7

 

$50.4

 

$61.4

Revisions in estimated cash flows
(10.1
)
 
4.3

 
(10.1
)
 
7.0

 
—

 
(2.7
)
Liabilities settled
(10.4
)
 
(23.5
)
 
(9.7
)
 
(13.1
)
 
(0.7
)
 
(10.4
)
Liabilities incurred
7.3

 
2.0

 
—

 
11.7

 
7.3

 
—

Accretion expense
6.2

 
6.0

 
4.0

 
3.8

 
2.2

 
2.1

Balance, December 31

$177.5

 

$184.5

 

$118.3

 

$134.1

 

$59.2

 

$50.4
WPL [Member]  
Schedule of Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations (AROs)
ASSET RETIREMENT OBLIGATIONS
Recognized AROs relate to legal obligations for the removal, closure or dismantlement of several assets including, but not limited to, wind farms, ash ponds, active ash landfills, solar generation and above ground storage tanks. Recognized AROs also include legal obligations for the management and final disposition of asbestos and polychlorinated biphenyls. AROs are recorded in “Other current liabilities” and “Other liabilities” on the balance sheets. Refer to Note 2 for information regarding regulatory assets related to AROs. A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
 
Alliant Energy
 
IPL
 
WPL
 
2018
 
2017
 
2018
 
2017
 
2018
 
2017
Balance, January 1

$184.5

 

$195.7

 

$134.1

 

$124.7

 

$50.4

 

$61.4

Revisions in estimated cash flows
(10.1
)
 
4.3

 
(10.1
)
 
7.0

 
—

 
(2.7
)
Liabilities settled
(10.4
)
 
(23.5
)
 
(9.7
)
 
(13.1
)
 
(0.7
)
 
(10.4
)
Liabilities incurred
7.3

 
2.0

 
—

 
11.7

 
7.3

 
—

Accretion expense
6.2

 
6.0

 
4.0

 
3.8

 
2.2

 
2.1

Balance, December 31

$177.5

 

$184.5

 

$118.3

 

$134.1

 

$59.2

 

$50.4