in 2017 , cash flows provided by operations increased $ 160 million , primarily due to an increase in net income after non-cash adjustments , including the impact of the enactment of the tcja , and an increase in cash flows from working capital . the main factors contributing to the net income increase are described in the 201cconsolidated results of operations 201d section and include higher operating revenues , partially offset by higher income taxes due to a $ 125 million re-measurement charge resulting from the impact of the change in the federal tax rate on the company 2019s deferred income taxes from the enactment of the tcja . the increase in non-cash activities was mainly attributable to the increase in deferred income taxes , as mentioned above , and an increase in depreciation and amortization due to additional utility plant placed in service . the change in working capital was principally due to ( i ) the timing of accounts payable and accrued liabilities , including the accrual recorded during 2016 for the binding global agreement in principle to settle claims associated with the freedom industries chemical spill in west virginia , ( ii ) a decrease in unbilled revenues as a result of our military services group achieving significant capital project milestones during 2016 , and ( iii ) a change in other current assets and liabilities , including the decrease in other current assets associated with the termination of our four forward starting swap agreements and timing of payments clearing our cash accounts . the company expects to make pension contributions to the plan trusts of up to $ 31 million in 2019 . in addition , we estimate that contributions will amount to $ 32 million , $ 29 million , $ 29 million and $ 29 million in 2020 , 2021 , 2022 and 2023 , respectively . actual amounts contributed could change materially from these estimates as a result of changes in assumptions and actual investment returns , among other factors . cash flows used in investing activities the following table provides a summary of the major items affecting our cash flows used in investing activities: .
what are expected pension contributions in millions for 2020 and 2021?
( a ) includes removal costs from property , plant and equipment retirements and proceeds from sale of assets . in 2018 and 2017 , cash flows used in investing activities increased primarily due to an increase in our regulated capital expenditures , principally from incremental investments associated with the replacement and renewal of our transmission and distribution infrastructure in our regulated businesses , as well as acquisitions in both our regulated businesses and market-based businesses , as discussed below . our infrastructure investment plan consists of both infrastructure renewal programs , where we replace infrastructure , as needed , and major capital investment projects , where we construct new water and wastewater treatment and delivery facilities to meet new customer growth and water quality regulations . our projected capital expenditures and other investments are subject to periodic review and revision to reflect changes in economic conditions and other factors. .