It depends on which sales sections were reported and if there were adjustments. If you only entered a summary for Box A or Box D transactions and there were NO adjustments, you don't have to mail it. But if you entered a summary for any other section (other than A or D) or you had adjustments in your Box A or Box D summary, you have to upload a PDF (only in TurboTax Online) or mail it in within 3 days. TurboTax will print out Form 8453 with instructions if you are required to mail in your 1099-B.
See Mailing in 8949 with 8453 - the IRS needs the details of your or adjusted transactions from your 1099-B.
In lieu of Form 8949, you can substitute copies of your year-end broker statements that show the individual transactions. You don't need to include unadjusted Box A or Box D transactions.
Thanks for the help. Just to confirm, I am using the desktop premier version, so I can not just upload the pdf, instead I have to mail the paper statements, right? It will be about hundreds of pages, :(
You will have to mail it. You cannot attach files to TurboTax Desktop. And if your 1099-B or list of transactions is hundreds of pages, you would probably have to mail it anyway, as the file would be too large to e-file. It's an IRS limitation, not TurboTax.