note 6 : allowance for uncollectible accounts the following table provides the changes in the allowances for uncollectible accounts for the years ended december 31: .
what was the decrease in the total balance as of december 31 2018 from 2017?
note 7 : regulatory assets and liabilities regulatory assets regulatory assets represent costs that are probable of recovery from customers in future rates . the majority of the regulatory assets earn a return . the following table provides the composition of regulatory assets as of december 31 : 2018 2017 deferred pension expense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $ 362 $ 285 removal costs recoverable through rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 269 regulatory balancing accounts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 113 san clemente dam project costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 89 debt expense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 67 purchase premium recoverable through rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 57 deferred tank painting costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 42 make-whole premium on early extinguishment of debt . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 27 other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 112 total regulatory assets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $ 1156 $ 1061 the company 2019s deferred pension expense includes a portion of the underfunded status that is probable of recovery through rates in future periods of $ 352 million and $ 270 million as of december 31 , 2018 and 2017 , respectively . the remaining portion is the pension expense in excess of the amount contributed to the pension plans which is deferred by certain subsidiaries and will be recovered in future service rates as contributions are made to the pension plan . removal costs recoverable through rates represent costs incurred for removal of property , plant and equipment or other retirement costs . regulatory balancing accounts accumulate differences between revenues recognized and authorized revenue requirements until they are collected from customers or are refunded . regulatory balancing accounts include low income programs and purchased power and water accounts . san clemente dam project costs represent costs incurred and deferred by the company 2019s utility subsidiary in california pursuant to its efforts to investigate alternatives and remove the dam due to potential earthquake and flood safety concerns . in june 2012 , the california public utilities commission ( 201ccpuc 201d ) issued a decision authorizing implementation of a project to reroute the carmel river and remove the san clemente dam . the project includes the company 2019s utility subsidiary in california , the california state conservancy and the national marine fisheries services . under the order 2019s terms , the cpuc has authorized recovery for .