Table of Contents Available-for-sale investments in an unrealized loss position that are not other-than-temporarily impaired: December 31, 2018 Less than 12 months  1 12 months or more  1 Total (Millions of dollars) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate bonds Corporate bonds $ 280 $ 3 $ 391 $ 11 $ 671 $ 14 Asset-backed securities 6 — 38 1 44 1 Mortgage-backed debt securities U.S. governmental agency 52 — 223 5 275 5 Commercial — — 14 1 14 1 Total $ 338 $ 3 $ 666 $ 18 $ 1,004 $ 21 December 31, 2017 Less than 12 months  1 12 months or more  1 Total (Millions of dollars) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate bonds Corporate bonds $ 312 $ 2 $ 38 $ — $ 350 $ 2 Mortgage-backed debt securities U.S. governmental agency 129 1 110 3 239 4 Equity securities Large capitalization value 129 5 14 2 143 7 Smaller company growth 17 1 1 — 18 1 Total $ 587 $ 9 $ 163 $ 5 $ 750 $ 14 1 Indicates length of time that individual securities have been in a continuous unrealized loss position. Corporate Bonds.  The unrealized losses on our investments in corporate bonds and asset-backed securities relate to changes in interest rates and credit-related yield spreads since time of purchase. We do not intend to sell the investments and it is not likely that we will be required to sell the investments before recovery of their amortized cost basis. We do not consider these investments to be other-than-temporarily impaired as of December 31, 2018. Mortgage-Backed Debt Securities. The unrealized losses on our investments in U.S. governmental agency mortgage-backed securities and commercial mortgage-backed securities relate to changes in interest rates and credit-related yield spreads since time of purchase. We do not intend to sell the investments and it is not likely that we will be required to sell the investments before recovery of their amortized cost basis. We do not consider these investments to be other-than-temporarily impaired as of December 31, 2018. The cost basis and fair value of the available-for-sale debt securities at December 31, 2018, by contractual maturity, is shown below. Expected maturities will differ from contractual maturities because borrowers may have the right to prepay and creditors may have the right to call obligations. 112