Fair Value Measurements - Schedule of Assets at Fair Value Recurring Basis (Details) - USD ($) $ in Millions | Sep. 30, 2024 | Dec. 31, 2023 | Sep. 30, 2023 |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | $ 1,508 | $ 1,647 | |
Other securities | 73 | 72 | |
Restricted cash and restricted cash equivalents | 693 | 534 | $ 580 |
U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 12 | 17 | |
Obligations of states, municipalities, and political subdivisions | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 64 | 66 | |
Commercial paper | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | | 14 | |
Non-U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 154 | 167 | |
Corporate debt | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1,005 | 1,085 | |
RMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 176 | 180 | |
CMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 27 | 33 | |
CDO/ABS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 70 | 85 | |
Level 1 | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Total investment securities | 57 | 54 | |
Restricted cash and restricted cash equivalents | 686 | 534 | |
Level 2 | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Total investment securities | 1,521 | 1,662 | |
Restricted cash and restricted cash equivalents | 7 | 0 | |
Level 3 | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Total investment securities | 3 | 3 | |
Restricted cash and restricted cash equivalents | 0 | 0 | |
Fair Value, Measurements, Recurring | | | |
Assets | | | |
Cash equivalents in mutual funds | 189 | 97 | |
Cash equivalents in securities | 5 | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1,508 | 1,647 | |
Other securities | 73 | 72 | |
Total investment securities | 1,581 | 1,719 | |
Restricted cash equivalents in mutual funds | 672 | 525 | |
Restricted cash and restricted cash equivalents | 7 | | |
Total | 2,454 | 2,341 | |
Fair Value, Measurements, Recurring | Total bonds | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 20 | 22 | |
Fair Value, Measurements, Recurring | U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 12 | 17 | |
Fair Value, Measurements, Recurring | Obligations of states, municipalities, and political subdivisions | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 64 | 66 | |
Fair Value, Measurements, Recurring | Commercial paper | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | | 14 | |
Fair Value, Measurements, Recurring | Non-U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 154 | 167 | |
Fair Value, Measurements, Recurring | Corporate debt | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1,005 | 1,085 | |
Other securities | 4 | 4 | |
Fair Value, Measurements, Recurring | RMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 176 | 180 | |
Fair Value, Measurements, Recurring | CMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 27 | 33 | |
Fair Value, Measurements, Recurring | CDO/ABS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 70 | 85 | |
Other securities | 16 | 18 | |
Fair Value, Measurements, Recurring | Preferred stock | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 15 | 16 | |
Fair Value, Measurements, Recurring | Common stock | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 38 | 34 | |
Fair Value, Measurements, Recurring | Level 1 | | | |
Assets | | | |
Cash equivalents in mutual funds | 189 | 97 | |
Cash equivalents in securities | 0 | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 6 | 6 | |
Other securities | 51 | 48 | |
Total investment securities | 57 | 54 | |
Restricted cash equivalents in mutual funds | 672 | 525 | |
Restricted cash and restricted cash equivalents | 0 | | |
Total | 918 | 676 | |
Fair Value, Measurements, Recurring | Level 1 | Total bonds | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 1 | U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 1 | Obligations of states, municipalities, and political subdivisions | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 1 | Commercial paper | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | | 0 | |
Fair Value, Measurements, Recurring | Level 1 | Non-U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 1 | Corporate debt | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 6 | 6 | |
Other securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 1 | RMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 1 | CMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 1 | CDO/ABS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 0 | 0 | |
Other securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 1 | Preferred stock | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 15 | 16 | |
Fair Value, Measurements, Recurring | Level 1 | Common stock | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 36 | 32 | |
Fair Value, Measurements, Recurring | Level 2 | | | |
Assets | | | |
Cash equivalents in mutual funds | 0 | 0 | |
Cash equivalents in securities | 5 | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1,501 | 1,640 | |
Other securities | 20 | 22 | |
Total investment securities | 1,521 | 1,662 | |
Restricted cash equivalents in mutual funds | 0 | 0 | |
Total | 1,533 | 1,662 | |
Fair Value, Measurements, Recurring | Level 2 | Total bonds | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 20 | 22 | |
Fair Value, Measurements, Recurring | Level 2 | U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 12 | 17 | |
Fair Value, Measurements, Recurring | Level 2 | Obligations of states, municipalities, and political subdivisions | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 64 | 66 | |
Fair Value, Measurements, Recurring | Level 2 | Commercial paper | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | | 14 | |
Fair Value, Measurements, Recurring | Level 2 | Non-U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 154 | 167 | |
Fair Value, Measurements, Recurring | Level 2 | Corporate debt | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 998 | 1,078 | |
Other securities | 4 | 4 | |
Fair Value, Measurements, Recurring | Level 2 | RMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 176 | 180 | |
Fair Value, Measurements, Recurring | Level 2 | CMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 27 | 33 | |
Fair Value, Measurements, Recurring | Level 2 | CDO/ABS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 70 | 85 | |
Other securities | 16 | 18 | |
Fair Value, Measurements, Recurring | Level 2 | Preferred stock | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 2 | Common stock | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 3 | | | |
Assets | | | |
Cash equivalents in mutual funds | 0 | 0 | |
Cash equivalents in securities | 0 | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1 | 1 | |
Other securities | 2 | 2 | |
Total investment securities | 3 | 3 | |
Restricted cash equivalents in mutual funds | 0 | 0 | |
Restricted cash and restricted cash equivalents | 0 | | |
Total | 3 | 3 | |
Fair Value, Measurements, Recurring | Level 3 | Total bonds | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 3 | U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 3 | Obligations of states, municipalities, and political subdivisions | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 3 | Commercial paper | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | | 0 | |
Fair Value, Measurements, Recurring | Level 3 | Non-U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 3 | Corporate debt | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1 | 1 | |
Other securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 3 | RMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 3 | CMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 3 | CDO/ABS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 0 | 0 | |
Other securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 3 | Preferred stock | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 3 | Common stock | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | $ 2 | $ 2 | |