An email from Katia Illarionova, an RT producer, discusses expenses for Mr. Flynn’s trip to Russia.The document provides new details about Mr. Flynn’s ties to Russian entities just over a month after being forced to resign following revelations that he had misled Vice President Mike Pence and other top White House officials about his conversations last year with the Russian ambassador to the United States.The letter, addressed to Mr. Trump; James B. Comey, the director of the Federal Bureau of Investigation; and Defense Secretary Jim Mattis, requested additional documents related to Mr. Flynn’s security clearances.The fees were apparently for speaking engagements by Mr. Flynn, a retired Army lieutenant general and former head of the Defense Intelligence Agency. The engagements occurred before he became an official adviser to Mr. Trump’s presidential campaign. Document: Oversight Committee Releases Documents on Flynn’s Trip to RussiaThe letter and supporting documents provide new details about a trip Mr. Flynn took to Moscow in December 2015 on behalf of RT. As part of that trip, RT paid him more than $45,000 to deliver a speech at an opulent gala hosted by the network, where he sat next to the Russian president, Vladimir V. Putin.That summer, according to an invoice included with the letters, Mr. Flynn also received $11,250 from a Russian cargo airline named Volga-Dnepr Airlines.According to Mr. Cummings’s letter, the company came under United Nations scrutiny after allegations of bribery surfaced involving two Russian officials serving at the United Nations. As part of that investigation, the United Nations removed the company in 2007 from its approved list of vendors, the letter said.