Fair Value Measurements - Assets at Fair Value Recurring Basis (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020 |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | $ 1,907 | $ 1,847 |
Other securities | 85 | 75 |
U.S. government and government sponsored entities | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 16 | 12 |
Obligations of states, municipalities, and political subdivisions | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 79 | 92 |
Corporate debt | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 1,302 | 1,218 |
RMBS | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 170 | 215 |
CMBS | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 45 | 58 |
CDO/ABS | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 90 | 78 |
Level 1 | | |
Investments, Debt and Equity Securities [Abstract] | | |
Total investment securities | 59 | 44 |
Level 2 | | |
Investments, Debt and Equity Securities [Abstract] | | |
Total investment securities | 1,927 | 1,870 |
Level 3 | | |
Investments, Debt and Equity Securities [Abstract] | | |
Total investment securities | 6 | 8 |
Fair Value, Measurements, Recurring | | |
Assets | | |
Cash equivalents in mutual funds | 41 | 2,018 |
Cash equivalents in securities | 6 | 17 |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 1,907 | 1,847 |
Other securities | 85 | 75 |
Total investment securities | 1,992 | 1,922 |
Restricted cash equivalents in mutual funds | 468 | 441 |
Total | 2,507 | 4,398 |
Fair Value, Measurements, Recurring | Total bonds | | |
Investments, Debt and Equity Securities [Abstract] | | |
Other securities | 30 | 35 |
Fair Value, Measurements, Recurring | U.S. government and government sponsored entities | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 16 | 12 |
Fair Value, Measurements, Recurring | Obligations of states, municipalities, and political subdivisions | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 79 | 92 |
Fair Value, Measurements, Recurring | Commercial paper | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 50 | 28 |
Fair Value, Measurements, Recurring | Non-U.S. government and government sponsored entities | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 155 | 146 |
Other securities | | 1 |
Fair Value, Measurements, Recurring | Corporate debt | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 1,302 | 1,218 |
Other securities | 9 | 17 |
Fair Value, Measurements, Recurring | RMBS | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 170 | 215 |
Other securities | 1 | |
Fair Value, Measurements, Recurring | CMBS | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 45 | 58 |
Fair Value, Measurements, Recurring | CDO/ABS | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 90 | 78 |
Other securities | 20 | 17 |
Fair Value, Measurements, Recurring | Preferred stock | | |
Investments, Debt and Equity Securities [Abstract] | | |
Other securities | 22 | 13 |
Fair Value, Measurements, Recurring | Common stock | | |
Investments, Debt and Equity Securities [Abstract] | | |
Other securities | 33 | 27 |
Fair Value, Measurements, Recurring | Level 1 | | |
Assets | | |
Cash equivalents in mutual funds | 41 | 2,018 |
Cash equivalents in securities | 0 | 0 |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 5 | 5 |
Other securities | 54 | 39 |
Total investment securities | 59 | 44 |
Restricted cash equivalents in mutual funds | 468 | 441 |
Total | 568 | 2,503 |
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 |
Other securities | | 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 | |
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 | 22 | 13 |
Fair Value, Measurements, Recurring | Level 1 | Common stock | | |
Investments, Debt and Equity Securities [Abstract] | | |
Other securities | 32 | 26 |
Fair Value, Measurements, Recurring | Level 2 | | |
Assets | | |
Cash equivalents in mutual funds | 0 | 0 |
Cash equivalents in securities | 6 | 17 |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 1,897 | 1,836 |
Other securities | 30 | 34 |
Total investment securities | 1,927 | 1,870 |
Restricted cash equivalents in mutual funds | 0 | 0 |
Total | 1,933 | 1,887 |
Fair Value, Measurements, Recurring | Level 2 | Total bonds | | |
Investments, Debt and Equity Securities [Abstract] | | |
Other securities | 30 | 34 |
Fair Value, Measurements, Recurring | Level 2 | U.S. government and government sponsored entities | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 16 | 12 |
Fair Value, Measurements, Recurring | Level 2 | Obligations of states, municipalities, and political subdivisions | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 79 | 92 |
Fair Value, Measurements, Recurring | Level 2 | Commercial paper | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 50 | 28 |
Fair Value, Measurements, Recurring | Level 2 | Non-U.S. government and government sponsored entities | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 155 | 146 |
Other securities | | 1 |
Fair Value, Measurements, Recurring | Level 2 | Corporate debt | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 1,292 | 1,207 |
Other securities | 9 | 16 |
Fair Value, Measurements, Recurring | Level 2 | RMBS | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 170 | 215 |
Other securities | 1 | |
Fair Value, Measurements, Recurring | Level 2 | CMBS | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 45 | 58 |
Fair Value, Measurements, Recurring | Level 2 | CDO/ABS | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 90 | 78 |
Other securities | 20 | 17 |
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 | 5 | 6 |
Other securities | 1 | 2 |
Total investment securities | 6 | 8 |
Restricted cash equivalents in mutual funds | 0 | 0 |
Total | 6 | 8 |
Fair Value, Measurements, Recurring | Level 3 | Total bonds | | |
Investments, Debt and Equity Securities [Abstract] | | |
Other securities | 0 | 1 |
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 |
Other securities | | 0 |
Fair Value, Measurements, Recurring | Level 3 | Corporate debt | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 5 | 6 |
Other securities | 0 | 1 |
Fair Value, Measurements, Recurring | Level 3 | RMBS | | |
Investments, Debt and Equity Securities [Abstract] | | |
Available-for-sale securities | 0 | 0 |
Other securities | 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 | $ 1 | $ 1 |