The embattled speaker of Brazil's House of Representatives has vehemently denied reports that a document seized in a corruption probe suggests he received nearly $12 million to support legislation favoring a top investment bank.

In a late-night barrage of about 20 tweets on Sunday, Eduardo Cunha dismissed the reports as a "true absurdity," saying they appeared to be part of a plot against him.

The denials followed the publication Sunday of a story on the website of Rio de Janeiro's O Globo newspaper saying investigators seized the document implicating Cunha in the home of an aide to Sen. Delcidio do Amaral, the governing Workers' Party's leader in the Senate.

Amaral, his aide, Diogo Ferreira, billionaire banker Andre Esteves and an attorney were detained last week in connection with the mushrooming probe into corruption at Brazil's state-run oil giant Petrobras.

The report in O Globo said the document seized in Ferreira's residence stipulated that in exchange for passage of legislation favoring Esteves' BTG Pactual bank, the institution "paid Representative Eduardo Cunha the sum of $11.7 million." The note supposedly added that other lawmakers from Cunha's opposition party also received part of the bribe and that Cunha, Esteves and the others had a celebratory dinner together after the passage of the legislation, in March 2013.

In a statement, the bank denied making "any sort of payment" in exchange for support of the legislation, which centered around tax credits from failed banks.

The Federal Prosecutors' Office has not immediately responded to requests to confirm the information in O Globo's report.

In Sunday's tweets, Cunha said the report "smelled of a plot" against him. Speaking to reporters on Monday, he insisted the accusations made no sense because the amendment he backed would not have helped the bank.

Cunha already has been fighting for his political survival following the emergence of documents showing he held secret bank accounts in Switzerland. He's also the target of a separate investigation into allegations he took part in the sprawling corruption scheme at Petrobras.

Cunha maintains his innocence and has repeatedly insisted he won't step down as speaker of the house. Under Brazilian law, it's up to Cunha to decide whether to open impeachment proceedings against Brazilian President Dilma Rousseff, whose popularity has plunged amid the corruption scandals, an economic recession and a plunging currency. Rousseff has not been directly implicated in the corruption scheme.

Meanwhile Monday, BTG Pactual said in a statement that Esteves has resigned from his dual roles as chairman and CEO of the investment bank. The statement did not mention his detention, nor a ruling by the Supreme Court Sunday that Esteves could be detained indefinitely.

Esteves, Sen. Amaral, the lawmaker's aide and an attorney were detained their alleged roles in a scheme to scuttle the Petrobras corruption probe. Secret recordings suggest they were involved in a plot to keep former Petrobras director-turned-key finger-pointer Nestor Cervero from testifying against Amaral and Esteves.

BTG Pactual named Esteves' replacements on Monday, but the announcement did little to shore up shares in the bank, which have fallen precipitously since Wednesday's detentions.