The letter — a full unredacted version was submitted under seal — was in response to a question posed last week to lawyers for Deutsche Bank and Capital One, the two financial institutions that were issued subpoenas by House committees in April. Capital One also responded on Tuesday, saying it “does not possess any tax returns responsive to the Capital One subpoena.”

Mr. Trump’s tax returns have been a matter of intense curiosity since he declined to release them during the 2016 campaign, breaking with decades of candidate tradition. But a lawyer for the congressional committees said at last week’s hearing there was good reason to seek the documents.

The financial services committee, as part of an examination of money laundering in real estate, is looking at Mr. Trump’s finances to determine whether he helped Russians and other foreign buyers launder money through his properties, said the committees’ lawyer, Douglas Letter. He said the intelligence committee was trying to determine whether Mr. Trump’s financial dealings made him subject to foreign influence.

Deutsche Bank has long been Mr. Trump’s primary lender. For most years, it has only the first several pages of his tax returns, according to the current and former bank officials, but the bank possesses far more detailed financial data. That includes balance sheets, financial statements and documents detailing the organization of Mr. Trump’s web of businesses, the people said.

Congressional investigators believe those documents could be more helpful than the tax returns to understanding Mr. Trump’s web of businesses and sources of his money.