Fair Value Measurements - Assets at Fair Value Recurring Basis (Details) - USD ($) $ in Millions | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | $ 1,729 | $ 1,907 | |
Other securities | 71 | 85 | |
Restricted cash and restricted cash equivalents | 461 | 476 | $ 451 |
U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 16 | 16 | |
Obligations of states, municipalities, and political subdivisions | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 66 | 79 | |
Corporate debt | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1,137 | 1,302 | |
RMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 192 | 170 | |
CMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 35 | 45 | |
CDO/ABS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 86 | 90 | |
Level 1 | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Total investment securities | 51 | 59 | |
Restricted cash and restricted cash equivalents | 450 | 476 | |
Level 2 | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Total investment securities | 1,744 | 1,927 | |
Restricted cash and restricted cash equivalents | 11 | 0 | |
Level 3 | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Total investment securities | 5 | 6 | |
Restricted cash and restricted cash equivalents | 0 | 0 | |
Fair Value, Measurements, Recurring | | | |
Assets | | | |
Cash equivalents in mutual funds | 77 | 41 | |
Cash equivalents in securities | 17 | 6 | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1,729 | 1,907 | |
Other securities | 71 | 85 | |
Total investment securities | 1,800 | 1,992 | |
Restricted cash equivalents in mutual funds | 445 | 468 | |
Restricted cash and restricted cash equivalents | 11 | | |
Total | 2,350 | 2,507 | |
Fair Value, Measurements, Recurring | Total bonds | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 23 | 30 | |
Fair Value, Measurements, Recurring | U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 16 | 16 | |
Fair Value, Measurements, Recurring | Obligations of states, municipalities, and political subdivisions | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 66 | 79 | |
Fair Value, Measurements, Recurring | Commercial paper | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 55 | 50 | |
Fair Value, Measurements, Recurring | Non-U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 142 | 155 | |
Fair Value, Measurements, Recurring | Corporate debt | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1,137 | 1,302 | |
Other securities | 6 | 9 | |
Fair Value, Measurements, Recurring | RMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 192 | 170 | |
Other securities | 1 | 1 | |
Fair Value, Measurements, Recurring | CMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 35 | 45 | |
Fair Value, Measurements, Recurring | CDO/ABS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 86 | 90 | |
Other securities | 16 | 20 | |
Fair Value, Measurements, Recurring | Preferred stock | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 15 | 22 | |
Fair Value, Measurements, Recurring | Common stock | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 33 | 33 | |
Fair Value, Measurements, Recurring | Level 1 | | | |
Assets | | | |
Cash equivalents in mutual funds | 77 | 41 | |
Cash equivalents in securities | 0 | 0 | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 5 | 5 | |
Other securities | 46 | 54 | |
Total investment securities | 51 | 59 | |
Restricted cash equivalents in mutual funds | 445 | 468 | |
Restricted cash and restricted cash equivalents | 0 | | |
Total | 573 | 568 | |
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 | 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 | 5 | 5 | |
Other securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 1 | RMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 0 | 0 | |
Other 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 | 22 | |
Fair Value, Measurements, Recurring | Level 1 | Common stock | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 31 | 32 | |
Fair Value, Measurements, Recurring | Level 2 | | | |
Assets | | | |
Cash equivalents in mutual funds | 0 | 0 | |
Cash equivalents in securities | 17 | 6 | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1,721 | 1,897 | |
Other securities | 23 | 30 | |
Total investment securities | 1,744 | 1,927 | |
Restricted cash equivalents in mutual funds | 0 | 0 | |
Total | 1,772 | 1,933 | |
Fair Value, Measurements, Recurring | Level 2 | Total bonds | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 23 | 30 | |
Fair Value, Measurements, Recurring | Level 2 | U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 16 | 16 | |
Fair Value, Measurements, Recurring | Level 2 | Obligations of states, municipalities, and political subdivisions | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 66 | 79 | |
Fair Value, Measurements, Recurring | Level 2 | Commercial paper | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 55 | 50 | |
Fair Value, Measurements, Recurring | Level 2 | Non-U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 142 | 155 | |
Fair Value, Measurements, Recurring | Level 2 | Corporate debt | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1,129 | 1,292 | |
Other securities | 6 | 9 | |
Fair Value, Measurements, Recurring | Level 2 | RMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 192 | 170 | |
Other securities | 1 | 1 | |
Fair Value, Measurements, Recurring | Level 2 | CMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 35 | 45 | |
Fair Value, Measurements, Recurring | Level 2 | CDO/ABS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 86 | 90 | |
Other securities | 16 | 20 | |
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 | 0 | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 3 | 5 | |
Other securities | 2 | 1 | |
Total investment securities | 5 | 6 | |
Restricted cash equivalents in mutual funds | 0 | 0 | |
Restricted cash and restricted cash equivalents | 0 | | |
Total | 5 | 6 | |
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 | 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 | 3 | 5 | |
Other securities | 0 | 0 | |
Fair Value, Measurements, Recurring | Level 3 | RMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 0 | 0 | |
Other 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 | $ 1 | |