3.	CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES

Cash and cash equivalents primarily consist of deposits held at major banks, Tier-1 commercial paper and other securities with original maturities of 90 days or less. Marketable securities consist of Tier-1 commercial paper debt securities, corporate debt securities and certain other securities.

The amortized principal amounts of our cash, cash equivalents and marketable securities approximated their fair values at May 31, 2017 and 2016. We use the specific identification method to determine any realized gains or losses from the sale of our marketable securities classified as available-for-sale. Such realized gains and losses were insignificant for fiscal 2017, 2016 and 2015. The following table summarizes the components of our cash equivalents and marketable securities held, substantially all of which were classified as available-for-sale:

	May 31,
(in millions)	2017		2016
Corporate debt securities and other	$	41,618	$	35,488
Commercial paper debt securities		5,053		2,155
Money market funds		3,302		3,750
Total investments	$	49,973	$	41,393
Investments classified as cash equivalents	$	5,679	$	5,420
Investments classified as marketable securities	$	44,294	$	35,973

As of May 31, 2017 and 2016, approximately 32% and 28%, respectively, of our marketable securities investments mature within one year and 68% and 72%, respectively, mature within one to five years. Our investment portfolio is subject to market risk due to changes in interest rates. As described above, we limit purchases of marketable debt securities to investment-grade securities, which have high credit ratings and also limit the amount of credit exposure to any one issuer. As stated in our investment policy, we are averse to principal loss and seek to preserve our invested funds by limiting default risk and market risk.

Restricted cash that was included within cash and cash equivalents as presented within our consolidated balance sheets as of May 31, 2017 and May 31, 2016 and our consolidated statements of cash flows for the years ended May 31, 2017, May 31, 2016 and May 31, 2015 was nominal.