| Fair Value, Assets Measured on Recurring Basis |
The following tables summarize our assets measured at fair value on a recurring basis and the classification by level of input within the fair value hierarchy (in millions): | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Fair Value Measurement at Reporting Date Using | | Description | | March 31, 2024 | | Quoted Prices in Active Markets for Identical Assets
(Level 1) | | Significant Other Observable Inputs
(Level 2) | | Significant Unobservable Inputs
(Level 3) | | Cash | | $ | 6,495 | | | | | | | | | Cash equivalents: | | | | | | | | | | Money market funds | | 24,465 | | | $ | 24,465 | | | $ | — | | | $ | — | | | U.S. government and agency securities | | 808 | | | 808 | | | — | | | — | | | | | | | | | | | | Time deposits | | 350 | | | — | | | 350 | | | — | | | Corporate debt securities | | 189 | | | — | | | 189 | | | — | | | Total cash and cash equivalents | | 32,307 | | | 25,273 | | | 539 | | | — | | | Marketable securities: | | | | | | | | | | U.S. government securities | | 10,345 | | | 10,345 | | | — | | | — | | | U.S. government agency securities | | 3,468 | | | 3,468 | | | — | | | — | | | Corporate debt securities | | 12,000 | | | — | | | 12,000 | | | — | | | | | | | | | | | | Total marketable securities | | 25,813 | | | 13,813 | | | 12,000 | | | — | | | Restricted cash equivalents | | 858 | | | 858 | | | — | | | — | | | Other assets | | 101 | | | — | | | — | | | 101 | | | Total | | $ | 59,079 | | | $ | 39,944 | | | $ | 12,539 | | | $ | 101 | |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Fair Value Measurement at Reporting Date Using | | Description | | December 31, 2023 | | Quoted Prices in Active Markets for Identical Assets
(Level 1) | | Significant Other Observable Inputs
(Level 2) | | Significant Unobservable Inputs
(Level 3) | | Cash | | $ | 6,265 | | | | | | | | | Cash equivalents: | | | | | | | | | | Money market funds | | 32,910 | | | $ | 32,910 | | | $ | — | | | $ | — | | | U.S. government and agency securities | | 2,206 | | | 2,206 | | | — | | | — | | | | | | | | | | | | Time deposits | | 261 | | | — | | | 261 | | | — | | | Corporate debt securities | | 220 | | | — | | | 220 | | | — | | | Total cash and cash equivalents | | 41,862 | | | 35,116 | | | 481 | | | — | | | Marketable securities: | | | | | | | | | | U.S. government securities | | 8,439 | | | 8,439 | | | — | | | — | | | U.S. government agency securities | | 3,498 | | | 3,498 | | | — | | | — | | | Corporate debt securities | | 11,604 | | | — | | | 11,604 | | | — | | | | | | | | | | | | Total marketable securities | | 23,541 | | | 11,937 | | | 11,604 | | | — | | | Restricted cash equivalents | | 857 | | | 857 | | | — | | | — | | | Other assets | | 101 | | | — | | | — | | | 101 | | | Total | | $ | 66,361 | | | $ | 47,910 | | | $ | 12,085 | | | $ | 101 | |
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| Available-for-sale Marketable Securities |
The following tables summarize our available-for-sale marketable debt securities and cash equivalents with unrealized losses as of March 31, 2024 and December 31, 2023, aggregated by major security type and the length of time that individual securities have been in a continuous loss position (in millions): | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | March 31, 2024 | | Less than 12 months | | 12 months or greater | | Total | | Fair Value | | Unrealized Losses | | Fair Value | | Unrealized Losses | | Fair Value | | Unrealized Losses | | U.S. government securities | $ | 3,098 | | | $ | (11) | | | $ | 5,825 | | | $ | (278) | | | $ | 8,923 | | | $ | (289) | | | U.S. government agency securities | 447 | | | (1) | | | 3,108 | | | (146) | | | 3,555 | | | (147) | | | Corporate debt securities | 882 | | | (4) | | | 9,302 | | | (450) | | | 10,184 | | | (454) | | | Total | $ | 4,427 | | | $ | (16) | | | $ | 18,235 | | | $ | (874) | | | $ | 22,662 | | | $ | (890) | |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | December 31, 2023 | | Less than 12 months | | 12 months or greater | | Total | | Fair Value | | Unrealized Losses | | Fair Value | | Unrealized Losses | | Fair Value | | Unrealized Losses | | U.S. government securities | $ | 336 | | | $ | (1) | | | $ | 7,041 | | | $ | (275) | | | $ | 7,377 | | | $ | (276) | | | U.S. government agency securities | 71 | | | — | | | 3,225 | | | (164) | | | 3,296 | | | (164) | | | Corporate debt securities | 647 | | | (3) | | | 10,125 | | | (491) | | | 10,772 | | | (494) | | | Total | $ | 1,054 | | | $ | (4) | | | $ | 20,391 | | | $ | (930) | | | $ | 21,445 | | | $ | (934) | |
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