Affordable Care Act (Details) - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Affordable Care Act [Abstract] | ||
| Risk adjustment and reinsurance, pre-tax benefit, period increase (decrease) | $ 48 | $ 51 |
| Charge for uncertainty associated with collectibility of CSR Receivables | (22) | |
| Risk adjustment | (677) | (425) |
| Reinsurance | 15 | 122 |
| Risk corridor | 6 | (3) |
| Minimum MLR | 22 | 18 |
| Cost sharing reductions | $ (96) | $ (147) |