On the campaign trail, Donald J. Trump, the Republican presidential nominee, has sold himself as a businessman who has made billions of dollars and is beholden to no one.

But an investigation by The New York Times into the financial maze of Mr. Trump’s real estate holdings in the United States reveals that companies he owns have at least $650 million in debt — twice the amount than can be gleaned from public filings he has made as part of his bid for the White House. The Times’s inquiry also found that Mr. Trump’s fortunes depend deeply on a wide array of financial backers, including one he has cited in attacks during his campaign.

For example, an office building on Avenue of the Americas in Manhattan, of which Mr. Trump is part owner, carries a $950 million loan. Among the lenders: the Bank of China, one of the largest banks in a country that Mr. Trump has railed against as an economic foe of the United States, and Goldman Sachs, a financial institution he has said controls Hillary Clinton, the Democratic nominee, after it paid her $675,000 in speaking fees.

Real estate projects often involve complex ownership and mortgage structures. And given Mr. Trump’s long real estate career in the United States and abroad, as well as his claim that his personal wealth exceeds $10 billion, it is safe to say that no previous major party presidential nominee has had finances nearly as complicated.