Marketable Securities - Additional Information (Details) - United States Government Agencies Corporate Debt Securities And Certificates Of Deposit [Member] $ in Millions |
Mar. 31, 2018
USD ($)
|
|---|---|
| Schedule of Available-for-sale Securities [Line Items] | |
| Marketable securities, maturing in one year or less | $ 29 |
| Marketable securities, maturing after one year through five years | 4 |
| Marketable securities, maturing after five years through ten years | $ 3 |