What does code "D" on line 1f of Form 8949 mean?

What does code "D" on line 1f of Form 8949 mean? I imported from Fidelity and code D is next to several U.S. Treasuries. For example, the proceeds is $10,000, the cost basis is $9,606, code d, gain is -394, and gain or loss is "0". Just want to make sure imported correctly and I should not be taxed?