table of contents valero energy corporation notes to consolidated financial statements ( continued ) 11 . equity share activity activity in the number of shares of common stock and treasury stock was as follows ( in millions ) : common treasury .
preferred stock we have 20 million shares of preferred stock authorized with a par value of $ 0.01 per share . no shares of preferred stock were outstanding as of december 31 , 2018 or 2017 . treasury stock we purchase shares of our common stock as authorized under our common stock purchase program ( described below ) and to meet our obligations under employee stock-based compensation plans . on july 13 , 2015 , our board of directors authorized us to purchase $ 2.5 billion of our outstanding common stock with no expiration date , and we completed that program during 2017 . on september 21 , 2016 , our board of directors authorized our purchase of up to an additional $ 2.5 billion with no expiration date , and we completed that program during 2018 . on january 23 , 2018 , our board of directors authorized our purchase of up to an additional $ 2.5 billion ( the 2018 program ) with no expiration date . during the years ended december 31 , 2018 , 2017 , and 2016 , we purchased $ 1.5 billion , $ 1.3 billion , and $ 1.3 billion , respectively , of our common stock under our programs . as of december 31 , 2018 , we have approval under the 2018 program to purchase approximately $ 2.2 billion of our common stock . common stock dividends on january 24 , 2019 , our board of directors declared a quarterly cash dividend of $ 0.90 per common share payable on march 5 , 2019 to holders of record at the close of business on february 13 , 2019 . valero energy partners lp units on september 16 , 2016 , vlp entered into an equity distribution agreement pursuant to which vlp offered and sold from time to time their common units having an aggregate offering price of up to $ 350 million based on amounts , at prices , and on terms determined by market conditions and other factors at the time of .
CommonStock TreasuryStock
Balance as of December 31, 2015 673 (200)
Transactions in connection withstock-based compensation plans — 1
Stock purchases under purchase program — (23)
Balance as of December 31, 2016 673 (222)
Transactions in connection withstock-based compensation plans — 1
Stock purchases under purchase programs — (19)
Balance as of December 31, 2017 673 (240)
Stock purchases under purchase programs — (16)
Balance as of December 31, 2018 673 (256)
commonstock treasurystock
balance as of december 31 2015 673 -200 ( 200 )
transactions in connection withstock-based compensation plans 2014 1
stock purchases under purchase program 2014 -23 ( 23 )
balance as of december 31 2016 673 -222 ( 222 )
transactions in connection withstock-based compensation plans 2014 1
stock purchases under purchase programs 2014 -19 ( 19 )
balance as of december 31 2017 673 -240 ( 240 )
stock purchases under purchase programs 2014 -16 ( 16 )
balance as of december 31 2018 673 -256 ( 256 )
how much , in billions , was spent purchasing common stock under the programs from 2016-2018?