The Clinton Foundation reported Thursday that it has received as much as $26.4 million in previously undisclosed payments from major corporations, universities, foreign sources and other groups. The disclosure came as the foundation faced questions over whether it fully complied with a 2008 ethics agreement to reveal its donors and whether any of its funding sources present conflicts of interest for Hillary Rodham Clinton as she begins her presidential campaign. The money was paid as fees for speeches by Bill, Hillary and Chelsea Clinton. Foundation officials said the funds were tallied internally as “revenue” rather than donations, which is why...