| **Investments - Schedule of Contractual Maturities of Investments (Details) - USD ($) $ in Millions** | Sep. 30, 2023 | Dec. 31, 2022 |
|-------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Amortized cost**                                                                                    |          |          |
| Due in one year or less                                                                               | $ 825         |          |
| Due after one year through five years                                                                 | 4,507         |          |
| Due after five years through ten years                                                                | 3,522         |          |
| Due after ten years                                                                                   | 5,196         |          |
| Total                                                                                                 | 14,050        | $ 12,979      |
| **Fair value**                                                                                        |          |          |
| Due in one year or less                                                                               | 814           |          |
| Due after one year through five years                                                                 | 4,314         |          |
| Due after five years through ten years                                                                | 3,246         |          |
| Due after ten years                                                                                   | 4,469         |          |
| Total                                                                                                 | $ 12,843      | $ 12,132      |
| **% of fair value**                                                                                   |          |          |
| Due in one year or less                                                                               | 6.30%         |          |
| Due after one year through five years                                                                 | 33.60%        |          |
| Due after five years through ten years                                                                | 25.30%        |          |
| Due after ten years                                                                                   | 34.80%        |          |
| Total                                                                                                 | 100.00%       |          |

| X                                                                                                                                                                                                                                                                                                                                                |
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| - Definition
Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).
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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).
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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).
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| - Definition
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| - Definition
Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing after tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).
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| - Definition
Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
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