Fair Value Measurements - Financial Instruments on a Recurring Basis (Details) - USD ($) $ in Millions | Sep. 30, 2024 | Dec. 31, 2023 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | $ 4,482 | $ 4,259 |
Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 2,848 | 2,732 |
Asset-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 438 | 365 |
Municipal securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 195 | 166 |
U.S. Treasury notes | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 5 | 40 |
Other | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 51 | 45 |
Fair value, recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total assets | 4,482 | 4,259 |
Fair value, recurring | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 2,848 | 2,732 |
Fair value, recurring | Mortgage-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 945 | 911 |
Fair value, recurring | Asset-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 438 | 365 |
Fair value, recurring | Municipal securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 195 | 166 |
Fair value, recurring | U.S. Treasury notes | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 5 | 40 |
Fair value, recurring | Other | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 51 | 45 |
Fair value, recurring | (Level 1) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total assets | 0 | 0 |
Fair value, recurring | (Level 1) | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 0 | 0 |
Fair value, recurring | (Level 1) | Mortgage-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 0 | 0 |
Fair value, recurring | (Level 1) | Asset-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 0 | 0 |
Fair value, recurring | (Level 1) | Municipal securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 0 | 0 |
Fair value, recurring | (Level 1) | U.S. Treasury notes | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 0 | 0 |
Fair value, recurring | (Level 1) | Other | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 0 | 0 |
Fair value, recurring | (Level 2) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total assets | 4,482 | 4,259 |
Fair value, recurring | (Level 2) | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 2,848 | 2,732 |
Fair value, recurring | (Level 2) | Mortgage-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 945 | 911 |
Fair value, recurring | (Level 2) | Asset-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 438 | 365 |
Fair value, recurring | (Level 2) | Municipal securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 195 | 166 |
Fair value, recurring | (Level 2) | U.S. Treasury notes | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 5 | 40 |
Fair value, recurring | (Level 2) | Other | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 51 | 45 |
Fair value, recurring | (Level 3) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total assets | 0 | 0 |
Fair value, recurring | (Level 3) | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 0 | 0 |
Fair value, recurring | (Level 3) | Mortgage-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 0 | 0 |
Fair value, recurring | (Level 3) | Asset-backed securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 0 | 0 |
Fair value, recurring | (Level 3) | Municipal securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 0 | 0 |
Fair value, recurring | (Level 3) | U.S. Treasury notes | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | 0 | 0 |
Fair value, recurring | (Level 3) | Other | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt securities, available-for-sale | $ 0 | $ 0 |