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Summary Of Significant Accounting Policies (Tables)
 12 Months Ended
Dec. 31, 2014
Schedule of Average Rates of Depreciation
The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:
 
IPL
 
WPL
 
2014
 
2013
 
2012
 
2014
 
2013 (a)
 
2012
Electric - generation
3.6%
 
3.6%
 
3.7%
 
3.2%
 
3.3%
 
3.2%
Electric - distribution
2.5%
 
2.5%
 
2.5%
 
2.7%
 
2.7%
 
2.9%
Gas
3.3%
 
3.4%
 
3.4%
 
2.5%
 
2.5%
 
2.6%
Other
4.2%
 
4.4%
 
4.5%
 
6.0%
 
5.1%
 
5.3%


(a)
In 2012, the PSCW issued an order approving the implementation of updated depreciation rates for WPL effective January 1, 2013 as a result of a recently completed depreciation study. In 2013, the PSCW and FERC issued orders approving WPL’s requests to revise depreciation rates associated with the acquisition of Riverside effective January 1, 2013.
Schedule of Allowance for Funds Used During Construction Recovery Rate
The AFUDC recovery rates, computed in accordance with the prescribed regulatory formula, were as follows:
 
2014
 
2013
 
2012
IPL (FERC formula - Marshalltown CWIP) (a)
8.0%
 
—%
 
—%
IPL (FERC formula - other CWIP)
7.8%
 
8.2%
 
8.2%
WPL (PSCW formula - retail jurisdiction)
8.2%
 
8.2%
 
8.8%
WPL (FERC formula - wholesale jurisdiction)
4.1%
 
4.5%
 
7.9%

(a)
In 2013, the IUB issued an order establishing rate-making principles for Marshalltown that requires a 10.3% return on common equity for the calculation of AFUDC related to the construction of such facility.
IPL [Member]  
Schedule of Average Rates of Depreciation
The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:
 
IPL
 
WPL
 
2014
 
2013
 
2012
 
2014
 
2013 (a)
 
2012
Electric - generation
3.6%
 
3.6%
 
3.7%
 
3.2%
 
3.3%
 
3.2%
Electric - distribution
2.5%
 
2.5%
 
2.5%
 
2.7%
 
2.7%
 
2.9%
Gas
3.3%
 
3.4%
 
3.4%
 
2.5%
 
2.5%
 
2.6%
Other
4.2%
 
4.4%
 
4.5%
 
6.0%
 
5.1%
 
5.3%


(a)
In 2012, the PSCW issued an order approving the implementation of updated depreciation rates for WPL effective January 1, 2013 as a result of a recently completed depreciation study. In 2013, the PSCW and FERC issued orders approving WPL’s requests to revise depreciation rates associated with the acquisition of Riverside effective January 1, 2013.
Schedule of Allowance for Funds Used During Construction Recovery Rate
The AFUDC recovery rates, computed in accordance with the prescribed regulatory formula, were as follows:
 
2014
 
2013
 
2012
IPL (FERC formula - Marshalltown CWIP) (a)
8.0%
 
—%
 
—%
IPL (FERC formula - other CWIP)
7.8%
 
8.2%
 
8.2%
WPL (PSCW formula - retail jurisdiction)
8.2%
 
8.2%
 
8.8%
WPL (FERC formula - wholesale jurisdiction)
4.1%
 
4.5%
 
7.9%

(a)
In 2013, the IUB issued an order establishing rate-making principles for Marshalltown that requires a 10.3% return on common equity for the calculation of AFUDC related to the construction of such facility.
WPL [Member]  
Schedule of Average Rates of Depreciation
The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:
 
IPL
 
WPL
 
2014
 
2013
 
2012
 
2014
 
2013 (a)
 
2012
Electric - generation
3.6%
 
3.6%
 
3.7%
 
3.2%
 
3.3%
 
3.2%
Electric - distribution
2.5%
 
2.5%
 
2.5%
 
2.7%
 
2.7%
 
2.9%
Gas
3.3%
 
3.4%
 
3.4%
 
2.5%
 
2.5%
 
2.6%
Other
4.2%
 
4.4%
 
4.5%
 
6.0%
 
5.1%
 
5.3%


(a)
In 2012, the PSCW issued an order approving the implementation of updated depreciation rates for WPL effective January 1, 2013 as a result of a recently completed depreciation study. In 2013, the PSCW and FERC issued orders approving WPL’s requests to revise depreciation rates associated with the acquisition of Riverside effective January 1, 2013.
Schedule of Allowance for Funds Used During Construction Recovery Rate
The AFUDC recovery rates, computed in accordance with the prescribed regulatory formula, were as follows:
 
2014
 
2013
 
2012
IPL (FERC formula - Marshalltown CWIP) (a)
8.0%
 
—%
 
—%
IPL (FERC formula - other CWIP)
7.8%
 
8.2%
 
8.2%
WPL (PSCW formula - retail jurisdiction)
8.2%
 
8.2%
 
8.8%
WPL (FERC formula - wholesale jurisdiction)
4.1%
 
4.5%
 
7.9%

(a)
In 2013, the IUB issued an order establishing rate-making principles for Marshalltown that requires a 10.3% return on common equity for the calculation of AFUDC related to the construction of such facility.