WASHINGTON (Reuters) - Former U.S. Vice President Joe Biden and his wife, Jill, earned more than $15 million in the two years after Biden left government in early 2017, according to tax records released by his campaign on Tuesday.

Former Vice President Joe Biden leaves the stage with his wife Jill after the conclusion of the second night of the first Democratic presidential candidates debate in Miami, Florida, U.S. June 27, 2019. REUTERS/Mike Segar

The majority of their income came from speaking engagements and payments for two books written by Biden, a top contender for the 2020 Democratic presidential nomination.

The former U.S. senator from Delaware served as Barack Obama’s vice president for eight years, leaving office in January 2017 after the election of Republican President Donald Trump.

According to federal and state tax returns, the Bidens earned about $11 million in 2017 and $4.58 million in 2018. About $13.2 million of that was attributable to book payments.

Biden earned more than $775,000 in salary as a professor at the University of Pennsylvania in 2017 and 2018.

The Biden campaign released a financial disclosure form mandated for presidential candidates, which provided details of his speaking engagements and book events from Jan. 1, 2018, to May 31, 2019.

The form shows that Biden, who likes to refer to himself as “Middle-Class Joe” on the campaign trail, was regularly paid a six-figure fee for speaking events, many at private universities such as Drew University, where he was paid $190,000, and Vanderbilt University, where he received $180,000.

Last October, Biden received $182,679 for speaking to the Economic Club of Southwest Michigan. In that speech, Biden drew flak from some Democrats for praising Republican U.S. Representative Fred Upton shortly before the 2018 congressional elections.

Most of Biden’s book events and speaking events took place at theaters and auditoriums, but two events were handled through Creative Artists Agency’s Premium Experience - which specializes in “corporate hospitality” events. For a CAA book tour event in 2017, Biden was paid $234,000.

The campaign did not provide any detailed information about Biden’s speaking engagements in 2017.

According to the couple’s tax returns, they paid $3.7 million in federal taxes in 2017 and donated about $1 million to charity. In 2018, they paid $1.5 million in federal taxes and donated about $275,000 to charity.