The subtraction for Interest on US Obligations refers to interest, dividend and gains that are taxable on your federal return but not on your Virginia return.
Examples of income not taxable in Virginia are:Tennessee Valley Authority, Federal Deposit Insurance Corporation; Federal Home Loan Bank; Federal Intermediate Credit Bank; Governments of Guam, Puerto Rico and Virgin Islands; U.S. Treasury bills, notes, bonds and savings bonds; Federal Land Bank; Federal Reserve Stock; Farm Credit Bank; Export-Import Bank of the U.S.; U.S. Postal Service; and Resolution Trust Corporation
Income that is taxable in Virginia include: Federal Home Loan Mortgage Corporation, Federal National Mortgage Association, Government National Mortgage Association, Inter-American Development Bank, and International Bank for Reconstruction and Development.
Please note these lists may not include all entities.