During FY2017, the federal government collected approximately $3.32 trillion in tax revenue, up $48 billion or 1.5% versus FY2016. Primary receipt categories included individual income taxes ($1,587B or 48% of total receipts), Social Security/Social Insurance taxes ($1,162B or 35%), and corporate taxes ($297B or 9%). Other revenue types included excise, estate and gift taxes. FY 2017 revenues were 17.3% of gross domestic product (GDP), versus 17.7% in FY 2016. Tax revenues averaged approximately 17.4% GDP over the 1980-2017 period.. Which was the second hightest reciept category?