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Investments (Tables) | 12 Months Ended
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Dec. 31, 2022
Investments [Abstract] |
Amortized Cost and Fair Value of the Trust Investments | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Amortized Costs | ​ | Fair Value
​ | ​ | Longest | ​ | December 31, | ​ | December 31, | ​ | December 31, | ​ | December 31,
(in millions) | ​ | Maturity Date |  | 2022 |  | 2021 |  | 2022 |  | 2021
Municipal bonds | ​ | 2061 |  | $ | 672 | ​ | $ | 875 | ​ | $ | 754 | ​ | $ | 1,033
Government and agency securities |  | 2072 |  | ​ | 1,025 |  | ​ | 1,095 | ​ |  | 1,091 | ​ |  | 1,212
Corporate bonds |  | 2070 |  | ​ | 351 |  | ​ | 386 | ​ |  | 377 | ​ |  | 446
Short-term investments and receivables/payables1 |  | One-year |  | ​ | 110 |  | ​ | 199 | ​ |  | 116 | ​ |  | 207
Total debt securities and other | ​ | ​ | ​ | $ | 2,158 | ​ | $ | 2,555 | ​ | ​ | 2,338 | ​ | ​ | 2,898
Equity securities | ​ | ​ |  | ​ | ​ |  | ​ | ​ | ​ | ​ | 1,610 | ​ | ​ | 1,972
Total |  |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | $ | 3,948 | ​ | $ | 4,870
1 | Short-term investments include $41 million and $37 million of repurchase agreements payable by financial institutions which earn interest, were 97% and fully secured by U.S. Treasury securities and mature by January 3, 2023 and January 3, 2022 as of December 31, 2022 and 2021, respectively.
Summary of gains and losses | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Years ended December 31,
(in millions) | ​ | 2022 |  | 2021 |  | 2020
Gross realized gains | ​ | $ | 150 | ​ | $ | 339 | ​ | $ | 255
Gross realized losses | ​ |  | (127) | ​ |  | (24) | ​ |  | (6)
Net unrealized (losses)/gains for equity securities | ​ |  | (369) | ​ |  | 103 | ​ |  | 176
Summarizes of unrealized gains/(losses) | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Years ended December 31,
(in millions) | ​ | 2022 |  | 2021 |  | 2020
Marketable securities | ​ | $ | (6) | ​ | $ | 3 | ​ | $ | —
Equity investments without readily determinable fair values - upward adjustments | ​ |  | 8 | ​ |  | 1 | ​ |  | —
Total unrealized gains | ​ | $ | 2 | ​ | $ | 4 | ​ | $ | —

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