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Marketable Securities Held in Trusts (Tables) | 9 Months Ended
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Sep. 30, 2024
Investments, Debt and Equity Securities [Abstract] |
Schedule of maturity dates for debt securities | The following table summarizes the balance by contractual maturity of the available-for-sale debt securities invested by the RCRA Trusts as of September 30, 2024. Actual maturities may differ from contractual maturities because the issuers of the securities may have the right to prepay obligations before the underlying contracts mature.
| September 30, 2024
Due in one year or less | $ | 24.1 |
Due after one year through five years | 275.3 |
Due after five years through ten years | 350.4 |
Due after ten years | 61.5 |
Total debt securities | $ | 711.3 |
Schedule of Unrealized Loss on Investments | The following tables show gross unrealized losses and fair values of the RCRA Trusts’ available-for-sale securities that have been in a continuous unrealized loss position for which an allowance for credit losses has not been recorded as of September 30, 2024 and December 31, 2023:
| September 30, 2024 |  | December 31, 2023
(in millions) | Fair Value |  | Gross Unrealized Losses |  | Fair Value |  | Gross Unrealized Losses
Securities that have been in a continuous loss position for less than 12 months: |  |  |  |  |  |  |
Corporate debt securities | $ | 5.3 |  |  | $ | — |  |  | $ | 5.4 |  |  | $ | (0.1) |
Municipal bonds | 25.7 |  |  | (0.2) |  |  | 42.3 |  |  | (0.2) |
U.S. government bonds | 6.4 |  |  | — |  |  | 26.4 |  |  | (0.3) |
| $ | 37.4 |  |  | $ | (0.2) |  |  | $ | 74.1 |  |  | $ | (0.6) |
Securities that have been in a continuous loss position for more than 12 months: |  |  |  |  |  |  |
Corporate debt securities | $ | 86.3 |  |  | $ | (4.8) |  |  | $ | 121.5 |  |  | $ | (8.3) |
Municipal bonds | 57.3 |  |  | (1.9) |  |  | 84.1 |  |  | (3.9) |
| $ | 143.6 |  |  | $ | (6.7) |  |  | $ | 205.6 |  |  | $ | (12.2) |
Unrealized Gain (Loss) on Investments | The estimated fair value of the investments in the RCRA Trusts as of September 30, 2024 and December 31, 2023 are as follows:
| September 30, 2024
| Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Value
Level 1 |  |  |  |  |  |  |
Cash and cash equivalents | $ | 1.9 |  |  | $ | — |  |  | $ | — |  |  | $ | 1.9 |
Level 2 |  |  |  |  |  |  |
Corporate debt securities | 202.6 |  |  | 3.6 |  |  | (4.8) |  |  | 201.4 |
Municipal bonds | 208.9 |  |  | 2.7 |  |  | (2.1) |  |  | 209.5 |
U.S. government bonds | 296.3 |  |  | 4.1 |  |  | — |  |  | 300.4 |
Total | $ | 709.7 |  |  | $ | 10.4 |  |  | $ | (6.9) |  |  | $ | 713.2 |
| December 31, 2023
| Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Value
Level 1 |  |  |  |  |  |  |
Cash and cash equivalents | $ | 1.0 |  |  | $ | — |  |  | $ | — |  |  | $ | 1.0 |
Level 2 |  |  |  |  |  |  |
Corporate debt securities | 204.6 |  |  | 1.9 |  |  | (8.4) |  |  | 198.1 |
Municipal bonds | 206.9 |  |  | 1.9 |  |  | (4.1) |  |  | 204.7 |
U.S. government bonds | 268.6 |  |  | 11.5 |  |  | (0.3) |  |  | 279.8 |
Total | $ | 681.1 |  |  | $ | 15.3 |  |  | $ | (12.8) |  |  | $ | 683.6 |

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