Investments - Available-for-Sale Investment Securities, Unrealized Gains and Losses (Details) - USD ($) $ in Millions |
Dec. 31, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Investment Identifier [Line Items] | ||
| Amortized Cost | $ 320 | $ 589 |
| Gross Unrealized Gain | 1 | 2 |
| Gross Unrealized Loss | 0 | 0 |
| Fair Value | 321 | 591 |
| Municipal securities | ||
| Investment Identifier [Line Items] | ||
| Amortized Cost | 10 | 15 |
| Gross Unrealized Gain | 0 | 0 |
| Gross Unrealized Loss | 0 | 0 |
| Fair Value | 10 | 15 |
| Government and agency securities | ||
| Investment Identifier [Line Items] | ||
| Amortized Cost | 64 | 108 |
| Gross Unrealized Gain | 0 | 0 |
| Gross Unrealized Loss | 0 | 0 |
| Fair Value | 64 | 108 |
| Corporate securities | ||
| Investment Identifier [Line Items] | ||
| Amortized Cost | 246 | 381 |
| Gross Unrealized Gain | 1 | 1 |
| Gross Unrealized Loss | 0 | 0 |
| Fair Value | 247 | 382 |
| Asset-backed securities | ||
| Investment Identifier [Line Items] | ||
| Amortized Cost | 0 | 85 |
| Gross Unrealized Gain | 0 | 1 |
| Gross Unrealized Loss | 0 | 0 |
| Fair Value | $ 0 | $ 86 |