Available-for-sale debt securities are recorded at fair value, with the portion of the unrealized gains and losses that are not credit-related included as a component of accumulated other comprehensive income (loss) in stockholders’ equity, until realized. Available-for-sale debt securities consisted of the following (in millions): | | | | | | | | | | | | | | | | | | | | | | | | As of September 30, 2024 | Amortized Cost | | Gross Unrealized Gains | | Gross Unrealized Losses | | Fair Value | U.S. government and agency securities | $ | 2,413.9 | | | $ | 11.4 | | | $ | (1.5) | | | $ | 2,423.8 | | Corporate debt securities | 602.8 | | | 4.8 | | | (0.7) | | | 606.9 | | | | | | | | | | Total | $ | 3,016.7 | | | $ | 16.2 | | | $ | (2.2) | | | $ | 3,030.7 | |
| | | | | | | | | | | | | | | | | | | | | | | | Reported under the following captions in our consolidated balance sheets: | Cash and cash equivalents | | | | | | | $ | 2.7 | | Current marketable investments | | | | | | | 1,748.6 | | Non-current marketable investments | | | | | | | 1,279.4 | | Total | | | | | | | $ | 3,030.7 | |
| | | | | | | | | | | | | | | | | | | | | | | | As of December 31, 2023 | Amortized Cost | | Gross Unrealized Gains | | Gross Unrealized Losses | | Fair Value | U.S. government and agency securities | $ | 3,044.5 | | | $ | 5.3 | | | $ | (17.2) | | | $ | 3,032.6 | | Corporate debt securities | 727.2 | | | 2.1 | | | (4.7) | | | 724.6 | | | | | | | | | | Total(1) | $ | 3,771.7 | | | $ | 7.4 | | | $ | (21.9) | | | $ | 3,757.2 | |
| | | | | | | | | | | | | | | | | | | | | | | | Reported under the following captions in our consolidated balance sheets: | Cash and cash equivalents | | | | | | | $ | 75.9 | | Current marketable investments | | | | | | | 1,771.5 | | Non-current marketable investments | | | | | | | 1,909.8 | | Total(1) | | | | | | | $ | 3,757.2 | |
(1)Total excludes $21.0 million related to available-for-sale debt securities that matured on December 31, 2023, although cash proceeds were not received until January 2, 2024. We recorded the $21.0 million receivable within other current assets in our consolidated balance sheets as of December 31, 2023.
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