IndexTax-exempt Money Market Funds [Member]
| Name | TaxexemptMoneyMarketFundsMember |
|---|---|
| Namespace | http://fasb.org/us-gaap/2020-01-31 |
| Prefix | us-gaap |
| Data type | nonnum:domainItemType |
| Period type | duration |
| Substitution Group | xbrli:item |
| Balance | None |
| Nillable | True |
| Abstract | True |
Labels
| Text | Lang | Role | Container role |
|---|---|---|---|
| Tax-exempt Money Market Funds [Member] | en-US | http://www.xbrl.org/2003/role/label | http://www.xbrl.org/2003/role/link |
| Investments in short-term tax-exempt money-market instruments, for example, but not limited to, commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and other highly liquid securities. | en-US | http://www.xbrl.org/2003/role/documentation | http://www.xbrl.org/2003/role/link |