If you want to play with the data on your own, you can download it as an Excel file here.
For fiscal year 2019, the complete U.S. federal budget was passed in three separate bills: H.R. 5895, H.R. 6157, and H.J.Res 31.
While those bills describe all discretionary spending in detail, they don't always show exact amounts for mandatory spending. To fill in the gaps for mandatory items, I referred to reports from the Congressional Research Service:
To double check larger mandatory items, such as Social Security, Medicare, and Medicaid, I referred to the Department of Health and Human Services FY 2019 budget request, as well as the 2019 values from the President's budget proposal for FY 2020. Since both documents are budget requests, their discretionary values should be ignored (since they don't necessarily match what Congress enacted), but their mandatory values are correct.
I referred to Wikipedia for descriptions of major agencies and sources of spending.
You can also check out last year's analysis.