U.S. Senate Democrats plan to enlist accountants and legal experts to pore through the business records of Exxon Mobil Chief Executive Rex Tillerson, President-elect Donald Trump's pick for secretary of state, Democratic aides said.

Tillerson could face a rocky confirmation process, given concerns among both Democrats and Republicans about his ties to Russia. If Tillerson can overcome the skepticism of Republicans, he could win confirmation since their party will control a slim majority in the Senate when Trump takes office on Jan. 20.

Democrats' misgivings about Tillerson go well beyond the worry that he might be too accommodating toward Moscow. They see risks of conflicts if the head of the $380 billion oil giant becomes the nation's top diplomat and they want to ensure that his personal wealth and business interests get close scrutiny.