united parcel service , inc . and subsidiaries management's discussion and analysis of financial condition and results of operations liquidity and capital resources as of december 31 , 2017 , we had $ 4.069 billion in cash , cash equivalents and marketable securities . we believe that our current cash position , access to the long-term debt capital markets and cash flow generated from operations should be adequate not only for operating requirements but also to enable us to complete our capital expenditure programs and to fund dividend payments , share repurchases and long-term debt payments through the next several years . in addition , we have funds available from our commercial paper program and the ability to obtain alternative sources of financing . we regularly evaluate opportunities to optimize our capital structure , including through issuances of debt to refinance existing debt and to fund ongoing cash needs . cash flows from operating activities the following is a summary of the significant sources ( uses ) of cash from operating activities ( amounts in millions ) : .
what was the difference in millions of pension and postretirement plan contributions ( ups-sponsored plans ) from 2015 to 2016?
( 1 ) represents depreciation and amortization , gains and losses on derivative transactions and foreign exchange , deferred income taxes , provisions for uncollectible accounts , pension and postretirement benefit expense , stock compensation expense and other non-cash items . cash from operating activities remained strong throughout 2015 to 2017 . most of the variability in operating cash flows during the 2015 to 2017 time period relates to the funding of our company-sponsored pension and postretirement benefit plans ( and related cash tax deductions ) . except for discretionary or accelerated fundings of our plans , contributions to our company- sponsored pension plans have largely varied based on whether any minimum funding requirements are present for individual pension plans . 2022 we made discretionary contributions to our three primary company-sponsored u.s . pension plans totaling $ 7.291 , $ 2.461 and $ 1.030 billion in 2017 , 2016 and 2015 , respectively . 2022 the remaining contributions from 2015 to 2017 were largely due to contributions to our international pension plans and u.s . postretirement medical benefit plans . apart from the transactions described above , operating cash flow was impacted by changes in our working capital position , payments for income taxes and changes in hedge margin payables and receivables . cash payments for income taxes were $ 1.559 , $ 2.064 and $ 1.913 billion for 2017 , 2016 and 2015 , respectively , and were primarily impacted by the timing of current tax deductions . the net hedge margin collateral ( paid ) /received from derivative counterparties was $ ( 732 ) , $ ( 142 ) and $ 170 million during 2017 , 2016 and 2015 , respectively , due to settlements and changes in the fair value of the derivative contracts used in our currency and interest rate hedging programs . as of december 31 , 2017 , the total of our worldwide holdings of cash , cash equivalents and marketable securities were $ 4.069 billion , of which approximately $ 1.800 billion was held by foreign subsidiaries . the amount of cash , cash equivalents and marketable securities held by our u.s . and foreign subsidiaries fluctuates throughout the year due to a variety of factors , including the timing of cash receipts and disbursements in the normal course of business . cash provided by operating activities in the u.s . continues to be our primary source of funds to finance domestic operating needs , capital expenditures , share repurchases and dividend payments to shareowners . as a result of the tax act , all cash , cash equivalents and marketable securities held by foreign subsidiaries are generally available for distribution to the u.s . without any u.s . federal income taxes . any such distributions may be subject to foreign withholding and u.s . state taxes . when amounts earned by foreign subsidiaries are expected to be indefinitely reinvested , no accrual for taxes is provided. .