Medical Claims and Benefits Payable - Additional Information (Details) - USD ($) $ in Millions |
3 Months Ended | ||
|---|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
Dec. 31, 2017 |
|
| Other Liabilities Disclosure [Abstract] | |||
| Non-risk provider payables | $ 146 | $ 122 | |
| Liability for Claims and Claims Adjustment Expense [Line Items] | |||
| Expense (recovery) for prior period claims development | $ 241 | $ 142 | |
| Minimum | |||
| Liability for Claims and Claims Adjustment Expense [Line Items] | |||
| Percentage of IBNP not expected to be paid | 8.00% | ||
| Maximum | |||
| Liability for Claims and Claims Adjustment Expense [Line Items] | |||
| Percentage of IBNP not expected to be paid | 10.00% | ||