Donald Trump and his business firms took-in more than $1.9 billion during his first three years as U.S. president from 2017 to 2019, despite Trump ostensibly yielding management of his companies to other people as required by U.S. law.

Of his various ventures, Trump's golf courses and clubs accounted for the largest chunk in revenues, $753 million, or 39% of his businesses' total income in these three years. His most profitable businesses, however, are his commercial real estate assets.

An in-depth report exposing Trump's billion dollar earnings while U.S. president are in the upcoming book, "White House, Inc." The tell-all was written by Dan Alexander, a senior editor at Forbes who covers Trump's businesses.

Quoting from his book in a story published in Forbes, Alexander said Trump held onto ownership of his assets and didn't divest from his business empire. Before his inauguration as president on Jan. 20, 2017, Trump handed over control of his companies to sons Eric and Donald Jr., along with his longtime Chief Financial Officer Allen Weisselberg.

Trump's assets, including commercial real estate, licensing businesses and cash holdings, were transferred to a trust under the control of his sons and Weisselberg. This arrangement ensured Trump would continue to earn money while serving as U.S. president. Trump continues to profit heavily from this arrangement today.

Documents obtained by Alexander show just how much the Trump companies profited from 2017 to 2019. It also reveals a clearer picture of Trump's business interests. Trump derives revenue from commercial building rentals, licensing agreements and his golf courses and club businesses.

Trump's golf courses and clubs accounted for most of the money he made over the last three year: $753 million. The most lucrative of his golf courses is the Trump National Doral golf resort in Miami, Florida, which earned $228 million in revenue from 2017 to 2019. Doral's revenue accounted for three-quarters of the total from the 10 other golf courses Trump owns in the United States.

In Europe, the Trump Turnberry golf resort generated $70 million. Trump's holdings in Doonbeg, Ireland and Aberdeenshire, Scotland earned him $53 million. Mar-a-Lago posted revenues of $69 million.

On the other hand, Trump's licensing, management and hotel business are on the decline. Trump's commercial buildings remain his most profitable.

Trump's commercial real estate assets posted profits of $313 million from 2017 to 2019, making them far more lucrative than his golf courses and clubs. His real estate holdings converted more than 50% of their revenue into profit.