allows us to repurchase shares at times when we may otherwise be prevented from doing so under insider trading laws or because of self-imposed trading blackout periods . subject to applicable regulations , we may elect to amend or cancel this repurchase program or the share repurchase parameters at our discretion . as of december 31 , 2018 , we have repurchased an aggregate of 4510000 shares of common stock under this program . credit facilities and short-term debt we have an unsecured revolving credit facility of $ 2.25 billion that expires in june 2023 . in march 2018 , awcc and its lenders amended and restated the credit agreement with respect to awcc 2019s revolving credit facility to increase the maximum commitments under the facility from $ 1.75 billion to $ 2.25 billion , and to extend the expiration date of the facility from june 2020 to march 2023 . all other terms , conditions and covenants with respect to the existing facility remained unchanged . subject to satisfying certain conditions , the credit agreement also permits awcc to increase the maximum commitment under the facility by up to an aggregate of $ 500 million , and to request extensions of its expiration date for up to two , one-year periods . interest rates on advances under the facility are based on a credit spread to the libor rate or base rate in accordance with moody investors service 2019s and standard & poor 2019s financial services 2019 then applicable credit rating on awcc 2019s senior unsecured , non-credit enhanced debt . the facility is used principally to support awcc 2019s commercial paper program and to provide up to $ 150 million in letters of credit . indebtedness under the facility is considered 201cdebt 201d for purposes of a support agreement between the company and awcc , which serves as a functional equivalent of a guarantee by the company of awcc 2019s payment obligations under the credit facility . awcc also has an outstanding commercial paper program that is backed by the revolving credit facility , the maximum aggregate outstanding amount of which was increased in march 2018 , from $ 1.60 billion to $ 2.10 billion . the following table provides the aggregate credit facility commitments , letter of credit sub-limit under the revolving credit facility and commercial paper limit , as well as the available capacity for each as of december 31 , 2018 and 2017 : credit facility commitment available credit facility capacity letter of credit sublimit available letter of credit capacity commercial paper limit available commercial capacity ( in millions ) december 31 , 2018 . . . . . . . . $ 2262 $ 2177 $ 150 $ 69 $ 2100 $ 1146 december 31 , 2017 . . . . . . . . 1762 1673 150 66 1600 695 the weighted average interest rate on awcc short-term borrowings for the years ended december 31 , 2018 and 2017 was approximately 2.28% ( 2.28 % ) and 1.24% ( 1.24 % ) , respectively . capital structure the following table provides the percentage of our capitalization represented by the components of our capital structure as of december 31: .

Table: 2018 2017 2016 total common shareholders' equity 40.4% ( 40.4 % ) 41.0% ( 41.0 % ) 42.1% ( 42.1 % ) long-term debt and redeemable preferred stock at redemption value 52.4% ( 52.4 % ) 49.6% ( 49.6 % ) 46.4% ( 46.4 % ) short-term debt and current portion of long-term debt 7.2% ( 7.2 % ) 9.4% ( 9.4 % ) 11.5% ( 11.5 % ) total 100% ( 100 % ) 100% ( 100 % ) 100% ( 100 % )

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Question: for the awcc commercial paper program that is backed by the revolving credit facility , what was the change in billions of the maximum aggregate outstanding amount from march 2018 , to december 2018?
Answer: 0.5
Calculation: subtract(2.10, 1.60)