State and local taxes greater than $10,000 is a negative number. What are the values that are used to calculate this number? Where can they be changed?

That’s right.  You can only deduct up to 10,000 for SALT State and Local Taxes

So the amount over 10,000 shows up as a negative number.  It doesn’t mean anything and doesn’t go anywhere.  Just for your info to let you know how much you can’t deduct this year.

This year the Standard Deduction will be doubling so many people will be switching to the Standard Deduction.  And there is a max 10,000 limit (5,000 MFS) of property tax and state taxes "SALT".

FAQ on 2018 changes https://ttlc.intuit.com/questions/4482394-how-will-tax-reform-affect-my-2018-federal-tax-return

For 2018 the standard deduction amounts are:
Single 12,000 + 1,600 for 65 and over or blind
HOH 18,000 + 1,600 for 65 and over or blind
Joint 24,000+ 1,300 for each 65 and over or blind
Married filing Separate 12,000 + 1,300 for 65 and over or blind

Oh it also includes any state withholding from your W2s and any 1099s.