Fair Value Measurements - Assets at Fair Value Recurring Basis (Details) - USD ($) $ in Millions | Mar. 31, 2023 | Dec. 31, 2022 | Mar. 31, 2022 |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | $ 1,716 | $ 1,729 | |
Other securities | 70 | 71 | |
Restricted cash and restricted cash equivalents | 531 | 461 | $ 531 |
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 | 67 | 66 | |
Corporate debt | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1,123 | 1,137 | |
RMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 190 | 192 | |
CMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 35 | 35 | |
CDO/ABS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 86 | 86 | |
Level 1 | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Total investment securities | 52 | 51 | |
Restricted cash and restricted cash equivalents | 531 | 450 | |
Level 2 | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Total investment securities | 1,729 | 1,744 | |
Restricted cash and restricted cash equivalents | 0 | 11 | |
Level 3 | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Total investment securities | 5 | 5 | |
Restricted cash and restricted cash equivalents | 0 | 0 | |
Fair Value, Measurements, Recurring | | | |
Assets | | | |
Cash equivalents in mutual funds | 109 | 77 | |
Cash equivalents in securities | 6 | 17 | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1,716 | 1,729 | |
Other securities | 70 | 71 | |
Total investment securities | 1,786 | 1,800 | |
Restricted cash equivalents in mutual funds | 517 | 445 | |
Restricted cash and restricted cash equivalents | | 11 | |
Total | 2,418 | 2,350 | |
Fair Value, Measurements, Recurring | Total bonds | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 21 | 23 | |
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 | 67 | 66 | |
Fair Value, Measurements, Recurring | Commercial paper | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 55 | 55 | |
Fair Value, Measurements, Recurring | Non-U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 144 | 142 | |
Fair Value, Measurements, Recurring | Corporate debt | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1,123 | 1,137 | |
Other securities | 5 | 6 | |
Fair Value, Measurements, Recurring | RMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 190 | 192 | |
Other securities | | 1 | |
Fair Value, Measurements, Recurring | CMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 35 | 35 | |
Fair Value, Measurements, Recurring | CDO/ABS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 86 | 86 | |
Other securities | 16 | 16 | |
Fair Value, Measurements, Recurring | Preferred stock | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 16 | 15 | |
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 | 109 | 77 | |
Cash equivalents in securities | 0 | 0 | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 5 | 5 | |
Other securities | 47 | 46 | |
Total investment securities | 52 | 51 | |
Restricted cash equivalents in mutual funds | 517 | 445 | |
Restricted cash and restricted cash equivalents | | 0 | |
Total | 678 | 573 | |
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 | |
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 | 16 | 15 | |
Fair Value, Measurements, Recurring | Level 1 | Common stock | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 31 | 31 | |
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 | 1,708 | 1,721 | |
Other securities | 21 | 23 | |
Total investment securities | 1,729 | 1,744 | |
Restricted cash equivalents in mutual funds | 0 | 0 | |
Restricted cash and restricted cash equivalents | | 11 | |
Total | 1,735 | 1,772 | |
Fair Value, Measurements, Recurring | Level 2 | Total bonds | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Other securities | 21 | 23 | |
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 | 67 | 66 | |
Fair Value, Measurements, Recurring | Level 2 | Commercial paper | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 55 | 55 | |
Fair Value, Measurements, Recurring | Level 2 | Non-U.S. government and government sponsored entities | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 144 | 142 | |
Fair Value, Measurements, Recurring | Level 2 | Corporate debt | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 1,115 | 1,129 | |
Other securities | 5 | 6 | |
Fair Value, Measurements, Recurring | Level 2 | RMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 190 | 192 | |
Other securities | | 1 | |
Fair Value, Measurements, Recurring | Level 2 | CMBS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 35 | 35 | |
Fair Value, Measurements, Recurring | Level 2 | CDO/ABS | | | |
Investments, Debt and Equity Securities [Abstract] | | | |
Available-for-sale securities | 86 | 86 | |
Other securities | 16 | 16 | |
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 | 3 | |
Other securities | 2 | 2 | |
Total investment securities | 5 | 5 | |
Restricted cash equivalents in mutual funds | 0 | 0 | |
Restricted cash and restricted cash equivalents | | 0 | |
Total | 5 | 5 | |
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 | 3 | |
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 | |
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 | |