valuation techniques 2013 cash equivalents are mostly comprised of short-term money-market instruments and are valued at cost , which approximates fair value .u.s .equity securities and international equity securities categorized as level 1 are traded on active national and international exchanges and are valued at their closing prices on the last trading day of the year .for u.s .equity securities and international equity securities not traded on an active exchange , or if the closing price is not available , the trustee obtains indicative quotes from a pricing vendor , broker or investment manager .these securities are categorized as level 2 if the custodian obtains corroborated quotes from a pricing vendor or categorized as level 3 if the custodian obtains uncorroborated quotes from a broker or investment manager .commingled equity funds categorized as level 1 are traded on active national and international exchanges and are valued at their closing prices on the last trading day of the year .for commingled equity funds not traded on an active exchange , or if the closing price is not available , the trustee obtains indicative quotes from a pricing vendor , broker or investment manager .these securities are categorized as level 2 if the custodian obtains corroborated quotes from a pricing vendor .fixed income investments categorized as level 2 are valued by the trustee using pricing models that use verifiable observable market data ( e.g. , interest rates and yield curves observable at commonly quoted intervals and credit spreads ) , bids provided by brokers or dealers or quoted prices of securities with similar characteristics .fixed income investments are categorized as level 3 when valuations using observable inputs are unavailable .the trustee typically obtains pricing based on indicative quotes or bid evaluations from vendors , brokers or the investment manager .in addition , certain other fixed income investments categorized as level 3 are valued using a discounted cash flow approach .significant inputs include projected annuity payments and the discount rate applied to those payments .certain commingled equity funds , consisting of equity mutual funds , are valued using the nav .the nav valuations are based on the underlying investments and typically redeemable within 90 days .private equity funds consist of partnership and co-investment funds .the nav is based on valuation models of the underlying securities , which includes unobservable inputs that cannot be corroborated using verifiable observable market data .these funds typically have redemption periods between eight and 12 years .real estate funds consist of partnerships , most of which are closed-end funds , for which the nav is based on valuation models and periodic appraisals .these funds typically have redemption periods between eight and 10 years .hedge funds consist of direct hedge funds for which the nav is generally based on the valuation of the underlying investments .redemptions in hedge funds are based on the specific terms of each fund , and generally range from a minimum of one month to several months .contributions and expected benefit payments the funding of our qualified defined benefit pension plans is determined in accordance with erisa , as amended by the ppa , and in a manner consistent with cas and internal revenue code rules .we made contributions of $ 5.0 billion to our qualified defined benefit pension plans in 2018 , including required and discretionary contributions .as a result of these contributions , we do not expect to make contributions to our qualified defined benefit pension plans in 2019 .the following table presents estimated future benefit payments , which reflect expected future employee service , as of december 31 , 2018 ( in millions ) : .
[['', '2019', '2020', '2021', '2022', '2023', '2024 2013 2028'], ['qualified defined benefit pension plans', '$ 2350', '$ 2390', '$ 2470', '$ 2550', '$ 2610', '$ 13670'], ['retiree medical and life insurance plans', '170', '180', '180', '180', '170', '810']]
defined contribution plans we maintain a number of defined contribution plans , most with 401 ( k ) features , that cover substantially all of our employees .under the provisions of our 401 ( k ) plans , we match most employees 2019 eligible contributions at rates specified in the plan documents .our contributions were $ 658 million in 2018 , $ 613 million in 2017 and $ 617 million in 2016 , the majority of which were funded using our common stock .our defined contribution plans held approximately 33.3 million and 35.5 million shares of our common stock as of december 31 , 2018 and 2017. .

Question: what is the percentage change in 401 ( k ) contributions from 2016 to 2017?
Answer: -0.6%