For Form 1116, I'm told I need to provide a detailed explanation for Line 3B column a. Can anyone guide me on this?

[AmyC]

Yes, as you go through the program, you find description boxes. Those boxes  throughout the 1116 can become the required statements. In addition, the program may auto generate the statement for you depending on the source.

Take a look at your forms and be sure to view all worksheets and statements. You will see the statement listed.  To print or view  your forms, including all worksheets:

• In desktop, switch to Forms Mode. 
• For online:
  1. On the left side, select  Tax Tools
  2. Select Print center
  3. Select Print, save or preview this year's return
  4. If you have not paid, select pay now.

The IRS Form 1116 instructions require "Line 3b.

Enter on line 3b any other deductions that don't definitely relate to any specific type of income (for example, deductions shown on Schedule 1 (Form 1040), Part II, Adjustments to Income). Attach a statement listing the separate expenses included on lines 3a and 3b."