WASHINGTON — Rex W. Tillerson owns more than $50 million of Exxon Mobil stock, has earned an annual salary of $10 million and holds a range of positions — from director at the Boy Scouts of America to the managing director of a Texas horse and cattle ranch.

But Mr. Tillerson is prepared to resign from all those posts, sell all his stock and put much of his money into bland investments like Treasury bonds if he becomes secretary of state, according to an “ethics undertakings” memo he filed this week with the State Department. And, if he returns to the oil industry in the next decade, he could lose as much as $180 million.

The nine-page ethics letter detailing Mr. Tillerson’s commitments is the first of hundreds that will be made public in the coming weeks by members of President-elect Donald J. Trump’s cabinet and other top political appointees, presenting a historic test of the federal government’s ability to identify conflicts of interest — and figure out ways to avoid them.