The following table summarizes the Company's investments by major security type at March 31, 2024 (in millions): | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Cost | | Gross
Unrealized Gains /Upward Adjustments | | Gross
Unrealized Losses /Downward Adjustments | | Carrying Value | | Short-term investments: | | | | | | | | | | Debt securities: | | | | | | | | | | International government securities | | $ | 41 | | | $ | — | | | $ | — | | | $ | 41 | | U.S. government securities | | 106 | | | — | | | — | | | 106 | | | Corporate debt securities | | 216 | | | — | | | (1) | | | 215 | | | | | | | | | | | | Total short-term investments | | $ | 363 | | | $ | — | | | $ | (1) | | | $ | 362 | | | | | | | | | | | | Long-term investments: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Equity securities: | | | | | | | | | | Equity securities with readily determinable fair values | | $ | 715 | | | $ | — | | | $ | (420) | | | $ | 295 | | | Equity securities of private entities | | 97 | | | 259 | | | (208) | | | 148 | | | | | | | | | | | | Total long-term investments | | $ | 812 | | | $ | 259 | | | $ | (628) | | | $ | 443 | |
The following table summarizes the Company's investments by major security type at December 31, 2023 (in millions): | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Cost | | Gross
Unrealized Gains/Upward Adjustments | | Gross Unrealized Losses/Downward Adjustments | | Carrying Value | | Short-term investments: | | | | | | | | | | Debt securities: | | | | | | | | | | International government securities | | $ | 63 | | | $ | — | | | $ | — | | | $ | 63 | | U.S. government securities (1) | | 152 | | | — | | | (1) | | | 151 | | | Corporate debt securities | | 365 | | | — | | | (3) | | | 362 | | | | | | | | | | | | Total short-term investments | | $ | 580 | | | $ | — | | | $ | (4) | | | $ | 576 | | | | | | | | | | | | Long-term investments: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Equity securities: | | | | | | | | | | Equity securities with readily determinable fair values | | $ | 715 | | | $ | — | | | $ | (404) | | | $ | 311 | | | Equity securities of private entities | | 78 | | | 259 | | | (208) | | | 129 | | | | | | | | | | | | Total long-term investments | | $ | 793 | | | $ | 259 | | | $ | (612) | | | $ | 440 | |
(1) Includes investments in U.S. municipal bonds.
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