Which type of investment security is marked-to-market and reported as "Accumulated Other Comprehensive Income"?

The investment security classified as Available-for-Sale Securities is marked-to-market and reported in the financial statements as "Accumulated Other Comprehensive Income." This classification distinguishes these securities from trading securities, which are also marked to market but recognized in the income statement rather than comprehensive income. As for held-to-maturity securities, these are recorded at amortized cost and are not subject to market valuation, while marketable securities is a broader category that includes both trading and available-for-sale securities but does not define their reporting specifics.

Available-for-Sale Securities allow for fluctuations in their fair value to be recorded in a separate component of equity known as Accumulated Other Comprehensive Income until they are sold. This treatment helps avoid volatility in earnings resulting from temporary market changes while still providing transparency in reporting the fair value of these investments. Therefore, the emphasis on their treatment in comprehensive income makes this category distinct in investment accounting.