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Summary Of Significant Accounting Policies (Tables)
 12 Months Ended
Dec. 31, 2016
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
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
Electric - generation
3.5%
 
3.6%
 
3.6%
 
3.1%
 
3.2%
 
3.2%
Electric - distribution
2.4%
 
2.4%
 
2.5%
 
2.6%
 
2.7%
 
2.7%
Electric - other
4.2%
 
4.0%
 
4.0%
 
4.7%
 
4.5%
 
5.9%
Gas
3.3%
 
3.2%
 
3.3%
 
2.5%
 
2.5%
 
2.5%
Other
3.9%
 
3.9%
 
4.3%
 
5.9%
 
6.0%
 
6.0%
Schedule of Allowance for Funds Used During Construction Rate
The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
 
2016
 
2015
 
2014
IPL (Marshalltown CWIP) (a)
7.9%
 
7.9%
 
8.0%
IPL (other CWIP)
7.7%
 
7.7%
 
7.8%
WPL (retail jurisdiction)
8.2%
 
8.2%
 
8.2%
WPL (wholesale jurisdiction)
6.7%
 
7.9%
 
4.1%

(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
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
Electric - generation
3.5%
 
3.6%
 
3.6%
 
3.1%
 
3.2%
 
3.2%
Electric - distribution
2.4%
 
2.4%
 
2.5%
 
2.6%
 
2.7%
 
2.7%
Electric - other
4.2%
 
4.0%
 
4.0%
 
4.7%
 
4.5%
 
5.9%
Gas
3.3%
 
3.2%
 
3.3%
 
2.5%
 
2.5%
 
2.5%
Other
3.9%
 
3.9%
 
4.3%
 
5.9%
 
6.0%
 
6.0%
Schedule of Allowance for Funds Used During Construction Rate
The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
 
2016
 
2015
 
2014
IPL (Marshalltown CWIP) (a)
7.9%
 
7.9%
 
8.0%
IPL (other CWIP)
7.7%
 
7.7%
 
7.8%
WPL (retail jurisdiction)
8.2%
 
8.2%
 
8.2%
WPL (wholesale jurisdiction)
6.7%
 
7.9%
 
4.1%

(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
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
Electric - generation
3.5%
 
3.6%
 
3.6%
 
3.1%
 
3.2%
 
3.2%
Electric - distribution
2.4%
 
2.4%
 
2.5%
 
2.6%
 
2.7%
 
2.7%
Electric - other
4.2%
 
4.0%
 
4.0%
 
4.7%
 
4.5%
 
5.9%
Gas
3.3%
 
3.2%
 
3.3%
 
2.5%
 
2.5%
 
2.5%
Other
3.9%
 
3.9%
 
4.3%
 
5.9%
 
6.0%
 
6.0%
Schedule of Allowance for Funds Used During Construction Rate
The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
 
2016
 
2015
 
2014
IPL (Marshalltown CWIP) (a)
7.9%
 
7.9%
 
8.0%
IPL (other CWIP)
7.7%
 
7.7%
 
7.8%
WPL (retail jurisdiction)
8.2%
 
8.2%
 
8.2%
WPL (wholesale jurisdiction)
6.7%
 
7.9%
 
4.1%

(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.