Elon Musk said he has lined up $46.5 billion to fund his bid for Twitter Inc., TWTR 0.59% ▲ answering the biggest question that had loomed over his takeover offer.

In a regulatory filing, Mr. Musk also said he was considering taking his offer straight to Twitter shareholders, bypassing a board that appears dug in. Twitter said Thursday it was reviewing the newly detailed proposal.

The financing commitments—about half in bank debt and half in cash promised by Mr. Musk himself—lend credibility to what had, until now, looked more like a personal lark than a bona fide takeover play. When he lobbed in his bid last week, Mr. Musk didn’t say how he planned to pay for the deal, which is expensive even for the world’s richest man.