which, at fair value, were $17.4 billion , $12.4 billion , and $11.4 billion as of December 31, 2014 , 2013 , and 2012 . Cash and cash equivalents also reflects net proceeds from the issuance of $6.0 billion of long-term debt as of December 31, 2014. Amounts held in foreign currencies were $5.4 billion , $5.6 billion, and $5.1 billion as of December 31, 2014 , 2013 , and 2012 , and were primarily British Pounds, Chinese Yuan, Euros, and Japanese Yen. 

Cash provided by operating activities was $6.8 billion, $5.5 billion, and $4.2 billion in 2014, 2013 , and 2012 . Our operating cash flows result primarily from cash received from our consumer, seller, and enterprise customers, advertising agreements, and our co-branded credit card agreements, offset by cash payments we make for products and services, employee compensation (less amounts capitalized related to internal- use software that are reflected as cash used in investing activities), payment processing and related transaction costs, operating leases, and interest payments on our long-term obligations. Cash received from our consumer, seller, and enterprise customers, and other activities generally corresponds to our net sales. Because consumers primarily use credit cards to buy from us, our receivables from consumers settle quickly. The increase in operating cash flow in 2014, compared to the comparable prior year period, was primarily due to the increase in non-cash charges to net income, including depreciation, amortization, and stock-based compensation, partially offset by changes in working capital. The increase in operating cash flow in 2013, compared to the comparable prior year period, was primarily due to the increase in net income, excluding depreciation, amortization, and stock-based compensation, partially offset by changes in working capital. 

Cash provided by (used in) investing activities corresponds with cash capital expenditures, including leasehold improvements, internal-use software and website development costs, cash outlays for acquisitions, investments in other companies and intellectual property rights, and purchases, sales, and maturities of marketable securities. Cash provided by (used in) investing activities was $(5.1) billion, $(4.3) billion , and $(3.6) billion in 2014 , 2013 , and 2012 , with the variability caused primarily by changes in capital expenditures, purchases, maturities, and sales of marketable securities and other investments, and changes in cash paid for acquisitions. Cash capital expenditures were $4.9 billion, $3.4 billion , and $3.8 billion during 2014 , 2013 , and 2012 . In December 2012, we acquired 11 buildings comprising 1.8 million square feet of our previously leased corporate office space and three city blocks in Seattle, Washington for $1.4 billion. Excluding this acquisition, increases in capital expenditures primarily reflect additional capacity to support our fulfillment operations and additional investments in support of continued business growth due to investments in technology infrastructure, including AWS, during all three periods. We expect this trend to continue over time. Capital expenditures included $537 million, $493