Fair Value Measurements - Assets at Fair Value Recurring Basis (Details) - USD ($) $ in Millions | Mar. 31, 2019 | Dec. 31, 2018 |
Investment securities: | | |
Available-for-sale securities | $ 1,657 | $ 1,607 |
Other securities | 86 | 87 |
U.S. government and government sponsored entities | | |
Investment securities: | | |
Available-for-sale securities | 17 | 21 |
Obligations of states, municipalities, and political subdivisions | | |
Investment securities: | | |
Available-for-sale securities | 87 | 90 |
Certificates of deposit and commercial paper | | |
Investment securities: | | |
Available-for-sale securities | 59 | 63 |
Corporate debt | | |
Investment securities: | | |
Available-for-sale securities | 1,059 | 997 |
RMBS | | |
Investment securities: | | |
Available-for-sale securities | 141 | 128 |
CMBS | | |
Investment securities: | | |
Available-for-sale securities | 66 | 71 |
CDO/ABS | | |
Investment securities: | | |
Available-for-sale securities | 83 | 94 |
Level 1 | | |
Assets | | |
Cash equivalents in securities | 1,666 | 618 |
Investment securities: | | |
Total investment securities | 37 | 34 |
Level 2 | | |
Assets | | |
Cash equivalents in securities | 43 | 61 |
Investment securities: | | |
Total investment securities | 1,702 | 1,655 |
Level 3 | | |
Assets | | |
Cash equivalents in securities | 0 | 0 |
Investment securities: | | |
Total investment securities | 4 | 5 |
Fair Value, Measurements, Recurring | | |
Assets | | |
Cash equivalents in mutual funds | 1,033 | 426 |
Cash equivalents in securities | 43 | 61 |
Investment securities: | | |
Available-for-sale securities | 1,657 | 1,607 |
Other securities | 86 | 87 |
Total investment securities | 1,743 | 1,694 |
Restricted cash in mutual funds | 560 | 482 |
Total | 3,379 | 2,663 |
Fair Value, Measurements, Recurring | Total bonds | | |
Investment securities: | | |
Other securities | 41 | 46 |
Fair Value, Measurements, Recurring | U.S. government and government sponsored entities | | |
Investment securities: | | |
Available-for-sale securities | 17 | 21 |
Fair Value, Measurements, Recurring | Obligations of states, municipalities, and political subdivisions | | |
Investment securities: | | |
Available-for-sale securities | 87 | 90 |
Fair Value, Measurements, Recurring | Certificates of deposit and commercial paper | | |
Investment securities: | | |
Available-for-sale securities | 59 | 63 |
Fair Value, Measurements, Recurring | Non-U.S. government and government sponsored entities | | |
Investment securities: | | |
Available-for-sale securities | 145 | 143 |
Other securities | 1 | 1 |
Fair Value, Measurements, Recurring | Corporate debt | | |
Investment securities: | | |
Available-for-sale securities | 1,059 | 997 |
Other securities | 38 | 43 |
Fair Value, Measurements, Recurring | RMBS | | |
Investment securities: | | |
Available-for-sale securities | 141 | 128 |
Other securities | 1 | 1 |
Fair Value, Measurements, Recurring | CMBS | | |
Investment securities: | | |
Available-for-sale securities | 66 | 71 |
Fair Value, Measurements, Recurring | CDO/ABS | | |
Investment securities: | | |
Available-for-sale securities | 83 | 94 |
Other securities | 1 | 1 |
Fair Value, Measurements, Recurring | Preferred stock | | |
Investment securities: | | |
Other securities | 20 | 19 |
Fair Value, Measurements, Recurring | Common stock | | |
Investment securities: | | |
Other securities | 24 | 21 |
Fair Value, Measurements, Recurring | Other long-term investments | | |
Investment securities: | | |
Other securities | 1 | 1 |
Fair Value, Measurements, Recurring | Level 1 | | |
Assets | | |
Cash equivalents in mutual funds | 1,033 | 426 |
Cash equivalents in securities | 0 | 0 |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Other securities | 37 | 34 |
Total investment securities | 37 | 34 |
Restricted cash in mutual funds | 560 | 482 |
Total | 1,630 | 942 |
Fair Value, Measurements, Recurring | Level 1 | Total bonds | | |
Investment securities: | | |
Other securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | U.S. government and government sponsored entities | | |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Obligations of states, municipalities, and political subdivisions | | |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Certificates of deposit and commercial paper | | |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Non-U.S. government and government sponsored entities | | |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Other securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Corporate debt | | |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Other securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | RMBS | | |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Other securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | CMBS | | |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | CDO/ABS | | |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Other securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Preferred stock | | |
Investment securities: | | |
Other securities | 13 | 13 |
Fair Value, Measurements, Recurring | Level 1 | Common stock | | |
Investment securities: | | |
Other securities | 24 | 21 |
Fair Value, Measurements, Recurring | Level 1 | Other long-term investments | | |
Investment securities: | | |
Other securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 2 | | |
Assets | | |
Cash equivalents in mutual funds | 0 | 0 |
Cash equivalents in securities | 43 | 61 |
Investment securities: | | |
Available-for-sale securities | 1,655 | 1,604 |
Other securities | 47 | 51 |
Total investment securities | 1,702 | 1,655 |
Restricted cash in mutual funds | 0 | 0 |
Total | 1,745 | 1,716 |
Fair Value, Measurements, Recurring | Level 2 | Total bonds | | |
Investment securities: | | |
Other securities | 40 | 45 |
Fair Value, Measurements, Recurring | Level 2 | U.S. government and government sponsored entities | | |
Investment securities: | | |
Available-for-sale securities | 17 | 21 |
Fair Value, Measurements, Recurring | Level 2 | Obligations of states, municipalities, and political subdivisions | | |
Investment securities: | | |
Available-for-sale securities | 87 | 90 |
Fair Value, Measurements, Recurring | Level 2 | Certificates of deposit and commercial paper | | |
Investment securities: | | |
Available-for-sale securities | 59 | 63 |
Fair Value, Measurements, Recurring | Level 2 | Non-U.S. government and government sponsored entities | | |
Investment securities: | | |
Available-for-sale securities | 145 | 143 |
Other securities | 1 | 1 |
Fair Value, Measurements, Recurring | Level 2 | Corporate debt | | |
Investment securities: | | |
Available-for-sale securities | 1,057 | 995 |
Other securities | 37 | 42 |
Fair Value, Measurements, Recurring | Level 2 | RMBS | | |
Investment securities: | | |
Available-for-sale securities | 141 | 128 |
Other securities | 1 | 1 |
Fair Value, Measurements, Recurring | Level 2 | CMBS | | |
Investment securities: | | |
Available-for-sale securities | 66 | 71 |
Fair Value, Measurements, Recurring | Level 2 | CDO/ABS | | |
Investment securities: | | |
Available-for-sale securities | 83 | 93 |
Other securities | 1 | 1 |
Fair Value, Measurements, Recurring | Level 2 | Preferred stock | | |
Investment securities: | | |
Other securities | 7 | 6 |
Fair Value, Measurements, Recurring | Level 2 | Common stock | | |
Investment securities: | | |
Other securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 2 | Other long-term investments | | |
Investment securities: | | |
Other securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | | |
Assets | | |
Cash equivalents in mutual funds | 0 | 0 |
Cash equivalents in securities | 0 | 0 |
Investment securities: | | |
Available-for-sale securities | 2 | 3 |
Other securities | 2 | 2 |
Total investment securities | 4 | 5 |
Restricted cash in mutual funds | 0 | 0 |
Total | 4 | 5 |
Fair Value, Measurements, Recurring | Level 3 | Total bonds | | |
Investment securities: | | |
Other securities | 1 | 1 |
Fair Value, Measurements, Recurring | Level 3 | U.S. government and government sponsored entities | | |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Obligations of states, municipalities, and political subdivisions | | |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Certificates of deposit and commercial paper | | |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Non-U.S. government and government sponsored entities | | |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Other securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Corporate debt | | |
Investment securities: | | |
Available-for-sale securities | 2 | 2 |
Other securities | 1 | 1 |
Fair Value, Measurements, Recurring | Level 3 | RMBS | | |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Other securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | CMBS | | |
Investment securities: | | |
Available-for-sale securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | CDO/ABS | | |
Investment securities: | | |
Available-for-sale securities | 0 | 1 |
Other securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Preferred stock | | |
Investment securities: | | |
Other securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Common stock | | |
Investment securities: | | |
Other securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Other long-term investments | | |
Investment securities: | | |
Other securities | $ 1 | $ 1 |