WASHINGTON -- Joe Biden and his wife, Jill, took in more than $15 million since leaving the Obama White House, according to newly released documents, catapulting the Democratic presidential candidate into millionaire status and denting the working-class aura he's developed over decades.

Long fond of describing himself as "Middle Class Joe" while he took in little more than his government salary, the former vice-president stressed his working-class roots from the very beginning of his bid for his party's 2020 presidential nomination . But federal tax returns and a financial disclosure released Tuesday show that since Biden left public office, his income has surged thanks to a lucrative book deal and constant publicity tours that brought in more than $4 million.

Biden's disclosure showed that he also made at least $2.7 million in business income as part of his publicity tour and writing and took a $425,000 salary from CelticCapri Corp., the business entity the Bidens used for their post-White House work.

Since leaving the White House, Biden and his wife signed a multibook deal with Flatiron Books valued at $8 million, according to Publishers Weekly. Biden's first book , an account of his son Beau's death from cancer, briefly topped bestseller lists in 2017. He and his wife have also worked on two other book projects.

Biden earned $540,000 as a professor and namesake of the University of Pennsylvania's Penn Biden Center for Diplomacy and Global Engagement. Jill Biden made at least $700,000 in her own speaking engagements, the disclosure shows.

Joe Biden's basic speaking fee was reportedly $100,000 a speech, but his disclosure showed that while some appearances were priced as low as the $40,000 range, others ranged as high as $190,000 for a lecture at Drew University in New Jersey.

Biden's last financial disclosure, filed in 2016 during his final year as vice-president, showed that even after eight years at his $230,000-a-year government salary, Biden held significant personal debt. The 2016 disclosure revealed financial assets worth more than $273,000 -- including a $150,000 rental property -- and more than $750,000 in debt. Those liabilities included a recent mortgage worth more than $500,000 on the rental property and a recent $250,000 home equity loan.

But much of that debt has been paid off, according to the latest disclosure, which showed only two old loans, each worth no more than $15,000 and dating to the 1980s.

Biden's three newly available tax returns, for 2016, 2017 and 2018, show that his family income jumped from $400,000 in 2016 to $11 million in 2017 as a result of his book deal.

Biden's most recent federal tax return had been released by the Obama administration in 2015. He and Jill Biden paid $85,000 in federal taxes on $390,000 in income, which includes both their salaries and nearly $19,000 in rental income. The Bidens that year held less than $25,000 in investments and gave nearly $7,000 to charity.

The Bidens also donated between $100,000 and $499,000 to the Biden Foundation, a family based non-profit, since its launch in November 2016, according to the charity's website. The Bidens set up the non-profit to advance political and cultural issues aligned with his political interests, but the couple suspended the foundation's operations last April to concentrate on Biden's presidential campaign.