Capital Gains Tax Computation Smart Worksheet
Row A Schedule D, Line 7
This line is basically Net short-term capital gain or (loss) and can not handle negative numbers beyond --999,999 if trying to enter into supporting details table. For example, -1,000,000 (negative 1 million) will popup error window "This value is too large" It does work entering without using supporting details table.
Note these losses aren't necessarily losing this amount of money. Rather, its loss harvesting efforts that accumulates suspended losses to offset near future gains.