The amortized cost, gross unrealized holding losses and fair value of marketable securities, excluding accrued interest receivable, consisted of the following: | | | | | | | | | | | | | | | | | | | | September 30, 2023 | | Amortized Cost | | | Gross Unrealized Losses | | Fair Value | | Commercial paper | $ | 88 | | | | $ | — | | | $ | 88 | | | Certificates of deposit | 41 | | | | — | | | 41 | | | Corporate bonds | 71 | | | | — | | | 71 | | | U.S. government agency securities | 80 | | | | — | | | 80 | | | Treasury securities | 156 | | | | (2) | | | 154 | | | Asset-backed securities | 82 | | | | — | | | 82 | | | Total | $ | 518 | | | | $ | (2) | | | $ | 516 | |
| | | | | | | | | | | | | | | | | | | | | December 31, 2022 | | Amortized Cost | | | | Gross Unrealized Losses | | Fair Value | | Commercial paper | $ | 140 | | | | | $ | — | | | $ | 140 | | | Certificates of deposit | 104 | | | | | — | | | 104 | | | Corporate bonds | 110 | | | | | (1) | | | 109 | | | U.S. government agency securities | 33 | | | | | — | | | 33 | | | Treasury securities | 61 | | | | | (1) | | | 60 | | | Asset-backed securities | 28 | | | | | — | | | 28 | | | Total | $ | 476 | | | | | $ | (2) | | | $ | 474 | |
The fair values of marketable securities by contractual maturities at September 30, 2023:
| | | | | | | | September 30,
2023 | | Due within 1 year | $ | 340 | | | Due after 1 year through 5 years | 172 | | Due after 5 years and thereafter | 4 | | | | | Total marketable securities | $ | 516 | |
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