| Dec 31, 2019 | Dec 31, 2020 | Dec 31, 2021 | Dec 31, 2022 | Dec 31, 2023 | Dec 31, 2024 |
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| Cash and Cash Equivalents, at Carrying Value | 183 | 484 | 343 | 263 | 273 | 454 |
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| Restricted cash and investments | 13 | 4 | 1 | - | - | - |
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| Accounts Receivable, after Allowance for Credit Loss, Current | 671 | 699 | 598 | 717 | 916 | 1,100 |
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| Contract with Customer, Asset, after Allowance for Credit Loss, Current | 575 | 577 | 579 | 634 | 758 | 742 |
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| Prepaid Expense and Other Assets, Current | 84 | 81 | 111 | 106 | 191 | 167 |
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| Total current assets | 1,526 | 1,843 | 1,632 | 1,720 | 2,138 | 2,462 |
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| Property, Plant and Equipment, Net | 123 | 121 | 104 | 96 | 99 | 112 |
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| Right of use assets, operating leases | 233 | 210 | 183 | 155 | 159 | 153 |
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| Goodwill | 1,047 | 1,262 | 1,413 | 1,662 | 1,793 | 2,083 |
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| Investments in and advances to unconsolidated joint ventures | 69 | 69 | 111 | 107 | 128 | 139 |
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| Intangible assets, net | 260 | 246 | 208 | 254 | 276 | 350 |
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| Deferred tax assets | 130 | 130 | 134 | 138 | 140 | 133 |
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| Other noncurrent assets | 61 | 56 | 46 | 66 | 72 | 56 |
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| Total assets | 3,450 | 3,938 | 3,831 | 4,198 | 4,804 | 5,488 |
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| Accounts Payable, Current | 217 | 226 | 196 | 201 | 243 | 208 |
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| Accrued Expenses And Other Current Liabilities | 640 | 651 | 599 | 630 | 801 | 894 |
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| Contract with Customer, Liability, Current | 231 | 202 | 172 | 213 | 301 | 290 |
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| Short-term lease liabilities, operating leases | 50 | 54 | 56 | 59 | 59 | 53 |
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| Income taxes payable | 7 | 5 | 8 | 4 | 7 | 8 |
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| Short-term debt | - | - | - | - | - | 463 |
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| Total current liabilities | 1,144 | 1,187 | 1,031 | 1,108 | 1,411 | 1,916 |
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| Long-term employee incentives | 57 | 22 | 16 | 17 | 23 | 32 |
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| Long-term debt | 249 | 540 | 592 | 744 | 746 | 784 |
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| Long-term lease liabilities, operating leases | 204 | 182 | 149 | 111 | 118 | 114 |
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| Deferred tax liabilities | 10 | 12 | 11 | 12 | 10 | 11 |
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| Other long-term liabilities | 126 | 132 | 95 | 109 | 120 | 96 |
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| Total liabilities | 1,790 | 2,076 | 1,894 | 2,102 | 2,427 | 2,953 |
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| Common Stock, Value, Issued | 146 | 147 | 146 | 146 | 146 | 147 |
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| Treasury stock, 39,880,875 shares at cost | 934 | 899 | 867 | 845 | 827 | 815 |
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| Additional paid-in capital | 2,650 | 2,701 | 2,685 | 2,717 | 2,779 | 2,685 |
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| Retained earnings | -218 | -121 | -54 | 43 | 204 | 427 |
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| Accumulated other comprehensive loss | -14 | -14 | -10 | -18 | -15 | -27 |
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| Total Parsons Corporation shareholders' equity | 1,661 | 1,861 | 1,937 | 2,096 | 2,377 | 2,534 |
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| Noncontrolling interests | 31 | 48 | 36 | 52 | 90 | 118 |
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| Total shareholders' equity | 1,661 | 1,861 | 1,937 | 2,096 | 2,377 | 2,534 |
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| Total liabilities and shareholders' equity | 3,450 | 3,938 | 3,831 | 4,198 | 4,804 | 5,488 |
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