This excerpt taken from the CCL 10-K filed Jan 29, 2009.
We account for our marketable security investments as trading, available-for-sale or held-to-maturity securities. As of November 30, 2008 and 2007, our marketable security investments were not significant and we had $20 million and $5 million of unrealized holding losses at such dates, respectively. All income generated from these investments is recorded as interest income.
Purchases and sales of short-term investments included in our 2007 Consolidated Statement of Cash Flows consisted of investments with original maturities greater than three months with variable interest rates, which typically reset every 28 days. Despite the long-term nature of their stated contractual maturities, prior to November 30, 2007 we had the ability to quickly liquidate these securities so they were considered short-term investments.