We perform fair value measurements in accordance with FASB Accounting Standards Codification (ASC) 820, Fair Value Measurement. ASC 820 defines fair value as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities required to be recorded at their fair values, we consider the principal or most advantageous market in which we would transact and consider assumptions that market participants would use when pricing the assets or liabilities, such as inherent risk, transfer restrictions and risk of nonperformance.

ASC 820 establishes a fair value hierarchy that requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. An asset’s or a liability’s categorization within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement. ASC 820 establishes three levels of inputs that may be used to measure fair value:

Assets and Liabilities Measured at Fair Value on a Recurring Basis

Our assets and liabilities measured at fair value on a recurring basis, excluding accrued interest components, consisted of the following (Level 1 and Level 2 inputs are defined above):

We classify our marketable securities as available-for-sale debt securities at the time of purchase and reevaluate such classification as of each balance sheet date. Our marketable securities investments consist of Tier 1 commercial paper debt securities, corporate debt securities and certain other securities. Marketable securities as presented per our condensed consolidated balance sheets included securities with original maturities at the time of purchase greater than three months and the remainder of the securities were included in cash and cash equivalents. As of February 28, 2019 and May 31, 2018, approximately 23% and 26%, respectively, of our marketable securities investments mature within one year and 77% and 74%, respectively, mature within one to five years. Our valuation techniques used to measure the fair values of our instruments that were classified as Level 1 in the table above were derived from quoted market prices and active markets for these instruments that exist. Our valuation techniques used to measure the fair values of Level 2 instruments listed in the table above, the counterparties to which have high credit ratings, were derived from the following: non-binding market consensus prices that were corroborated by observable market data, quoted market prices for similar instruments, or pricing models, such as discounted cash flow techniques, with all significant inputs derived from or corroborated by observable market data including LIBOR-based yield curves, among others.

Based on the trading prices of the $56.0 billion and $58.0 billion of senior notes and the related fair value hedges that we had outstanding as of February 28, 2019 and May 31, 2018, respectively, the estimated fair values of the senior notes and the related fair value hedges using Level 2 inputs at February 28, 2019 and May 31, 2018 were $56.9 billion and $59.0 billion, respectively.