On the Overview tab, you may see an item labeled 'Cash, Money Market, and Margin' when you expand an account. This line item is the sum of all of your cash balances and your money market balances and holdings, less any margin balance. Note that your money market holdings are included in this line and will not be included individually on the Overview tab.
Similarly, on the Holdings tab, you will see 'Cash & Money Market' at the top which includes all of your cash balances and your money market balances and holdings. If you have a margin balance it will be listed separately under 'Margin'. Your money market *holdings* will be detailed below. Note that your cash balances and some of money market *balances* may not be detailed below.