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Marketable Securities Held in Trusts (Tables) | 12 Months Ended
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Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract] |
Available-for-sale securities | The estimated fair value of the investments in the RCRA Trusts as of December 31, 2020 and December 31, 2019 are as follows:
| December 31, 2020
(in millions) | Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Value
Level 1 |  |  |  |  |  |  |
Cash and cash equivalents | $ | 11.8 |  |  | $ | — |  |  | $ | — |  |  | $ | 11.8 |
Level 2 |  |  |  |  |  |  |
Corporate debt securities | 193.3 |  |  | 14.0 |  |  | — |  |  | 207.3 |
Municipal bonds | 190.5 |  |  | 8.8 |  |  | (0.3) |  |  | 199.0 |
U.S. government bonds | 300.7 |  |  | 4.7 |  |  | (0.1) |  |  | 305.3 |
Total | $ | 696.3 |  |  | $ | 27.5 |  |  | $ | (0.4) |  |  | $ | 723.4 |
| December 31, 2019
(in millions) | Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Value
Level 1 |  |  |  |  |  |  |
Cash and cash equivalents | $ | 3.4 |  |  | $ | — |  |  | $ | — |  |  | $ | 3.4 |
Level 2 |  |  |  |  |  |  |
Corporate debt securities | 194.2 |  |  | 5.8 |  |  | (0.1) |  |  | 199.9 |
Municipal bonds | 188.3 |  |  | 4.4 |  |  | (0.4) |  |  | 192.3 |
U.S. government bonds | 280.6 |  |  | 3.2 |  |  | (2.5) |  |  | 281.3 |
Total | $ | 666.5 |  |  | $ | 13.4 |  |  | $ | (3.0) |  |  | $ | 676.9 |
Fair value of available-for-sale debt securities in an unrealized loss position | 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 deemed to be temporary as of December 31, 2020 and December 31, 2019.
| December 31, 2020 |  | December 31, 2019
Securities that have been in a continuous loss position for less than 12 months (in millions): | Fair Value |  | Gross Unrealized Losses |  | Fair Value |  | Gross Unrealized Losses
Corporate debt securities | $ | 1.5 |  |  | $ | — |  |  | $ | 17.9 |  |  | $ | — |
Municipal bonds | 16.0 |  |  | (0.2) |  |  | 11.7 |  |  | (0.1) |
U.S. government bonds | 120.3 |  |  | (0.1) |  |  | 195.4 |  |  | (2.5) |
Total | $ | 137.8 |  |  | $ | (0.3) |  |  | $ | 225.0 |  |  | $ | (2.6) |
| December 31, 2020 |  | December 31, 2019
Securities that have been in a continuous loss position for more than 12 months (in millions): | Fair Value |  | Gross Unrealized Losses |  | Fair Value |  | Gross Unrealized Losses
Corporate debt securities | $ | — |  |  | $ | — |  |  | $ | 20.7 |  |  | $ | (0.1) |
Municipal bonds | 4.6 |  |  | (0.1) |  |  | 14.7 |  |  | (0.3) |
Total | $ | 4.6 |  |  | $ | (0.1) |  |  | $ | 35.4 |  |  | $ | (0.4) |
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 December 31, 2020. 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.
(in millions) | December 31, 2020
Due in one year or less | $ | 27.6 |
Due after one year through five years | 274.5 |
Due after five years through ten years | 367.3 |
Due after ten years | 42.2 |
Total debt securities | $ | 711.6 |

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- Definition Tabular disclosure of fair value of investments in debt and equity securities in an unrealized loss position categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
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- Definition Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities. + References No definition available. + Details
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