[widgeon13]

You will most likely get documentation from the financial company that held the shares for you or directly from GM, as long as you can provide evidence you purchased the stock it shouldn't be difficult to document the value when it restructured. It's a long term capital loss and you can only deduct a max of $3000 per year, I believe. You can carryover the loss to the next year if greater than 3K.

Check w/ an accountant before you submit your tax return.