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Fair Value Measurements - Fair Value of Investment Assets (Details) - USD ($) $ in Millions | Mar. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Investments at Fair Value | $ 121 | $ 181
Carrying Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Investments at Amortized Cost | 124 | 184
Level 1 | Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Investments at Fair Value | 0 | 80
Level 1 | Fair Value | Fixed Income Mutual Funds |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Investments at Fair Value | 0 | 80
Level 1 | Fair Value | Corporate Bonds |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Investments at Fair Value | 0 | 0
Level 1 | Fair Value | Government Securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Investments at Fair Value | 0 | 0
Level 2 | Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Investments at Fair Value | 121 | 101
Level 2 | Fair Value | Fixed Income Mutual Funds |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Investments at Fair Value | 0 | 0
Level 2 | Fair Value | Corporate Bonds |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Investments at Fair Value | 72 | 60
Level 2 | Fair Value | Government Securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Investments at Fair Value | 49 | 41
Total | Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Investments at Fair Value | 121 | 181
Total | Fair Value | Fixed Income Mutual Funds |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Investments at Fair Value | 0 | 80
Total | Fair Value | Corporate Bonds |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Investments at Fair Value | 72 | 60
Total | Fair Value | Government Securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Investments at Fair Value | $ 49 | $ 41

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