Alliant Energy Corp. customers in Iowa won't see any increase in their base electric rates through 2016, the company announced Tuesday. Credits will also be included in customer bills based on the three-year agreement filed with the Iowa Utilities Board. The credits will total $70 million in 2014, $25 million in 2015 and $10 million in 2016, and will appear in the energy cost portion of customers' bills. The agreement, which is subject to approval by the utilities board, will extend the electric base rate freeze that has been in effect since 2011. The company said it will have invested about $750 million between 2011 and 2014 in Iowa to improve electric reliability and the emissions profile of its generating stations. The agreement offsets the cost of those investments with savings from a new purchased power agreement from the Duane Arnold Energy Center nuclear plant that began in February. Iowa's other investor-owned utility, MidAmerican Energy Co., last month received preliminary approval from the Iowa Utilities Board for a $135.6 million electric rate increase, which will be phased in over the next three years.