borrowings reflect net proceeds received from the issuance of senior notes in june 2015 . see liquidity and capital resources below for additional information . in november 2015 , we repaid our $ 1 billion 0.90% ( 0.90 % ) senior notes upon maturity . in october 2015 , we announced an adjustment to our quarterly dividend . see capital requirements below for additional information . additions to property , plant and equipment are our most significant use of cash and cash equivalents . the following table shows capital expenditures related to continuing operations by segment and reconciles to additions to property , plant and equipment as presented in the consolidated statements of cash flows for 2015 , 2014 and 2013: .
by how much did additions to property plant and equipment decrease from 2013 to 2015?
( a ) reflects reimbursements earned from the governments of canada and alberta related to funds previously expended for quest ccs capital equipment . quest ccs was successfully completed and commissioned in the fourth quarter of 2015 . during 2014 , we acquired 29 million shares at a cost of $ 1 billion and in 2013 acquired 14 million shares at a cost of $ 500 million . there were no share repurchases in 2015 . see item 8 . financial statements and supplementary data 2013 note 23 to the consolidated financial statements for discussion of purchases of common stock . liquidity and capital resources on june 10 , 2015 , we issued $ 2 billion aggregate principal amount of unsecured senior notes which consist of the following series : 2022 $ 600 million of 2.70% ( 2.70 % ) senior notes due june 1 , 2020 2022 $ 900 million of 3.85% ( 3.85 % ) senior notes due june 1 , 2025 2022 $ 500 million of 5.20% ( 5.20 % ) senior notes due june 1 , 2045 interest on each series of senior notes is payable semi-annually beginning december 1 , 2015 . we used the aggregate net proceeds to repay our $ 1 billion 0.90% ( 0.90 % ) senior notes on november 2 , 2015 , and the remainder for general corporate purposes . in may 2015 , we amended our $ 2.5 billion credit facility to increase the facility size by $ 500 million to a total of $ 3.0 billion and extend the maturity date by an additional year such that the credit facility now matures in may 2020 . the amendment additionally provides us the ability to request two one-year extensions to the maturity date and an option to increase the commitment amount by up to an additional $ 500 million , subject to the consent of any increasing lenders . the sub-facilities for swing-line loans and letters of credit remain unchanged allowing up to an aggregate amount of $ 100 million and $ 500 million , respectively . fees on the unused commitment of each lender , as well as the borrowing options under the credit facility , remain unchanged . our main sources of liquidity are cash and cash equivalents , internally generated cash flow from operations , capital market transactions , our committed revolving credit facility and sales of non-core assets . our working capital requirements are supported by these sources and we may issue either commercial paper backed by our $ 3.0 billion revolving credit facility or draw on our $ 3.0 billion revolving credit facility to meet short-term cash requirements or issue debt or equity securities through the shelf registration statement discussed below as part of our longer-term liquidity and capital management . because of the alternatives available to us as discussed above , we believe that our short-term and long-term liquidity is adequate to fund not only our current operations , but also our near-term and long-term funding requirements including our capital spending programs , dividend payments , defined benefit plan contributions , repayment of debt maturities and other amounts that may ultimately be paid in connection with contingencies . general economic conditions , commodity prices , and financial , business and other factors could affect our operations and our ability to access the capital markets . a downgrade in our credit ratings could negatively impact our cost of capital and our ability to access the capital markets , increase the interest rate and fees we pay on our unsecured revolving credit facility , restrict our access to the commercial paper market , or require us to post letters of credit or other forms of collateral for certain .