Warren Buffett says he's not worried that Congress will go past the point of "extreme idiocy," and refuse to raise the debt ceiling before the Treasury Department runs out of cash later this month.

"We will go right up to the point of extreme idiocy, but we won't cross it," he said in an interview on CNBC Thursday morning.

Treasury Secretary Jack Lew says that if Treasury doesn't sell more bonds by Oct. 17, it won't be able to pay its bills, including the interest on debt that's already in the market.

Buffett had very harsh words for Republicans in Congress who are threatening not to raise the debt ceiling unless Obamacare is delayed or defunded. Buffett said if that deadline is missed by just a short period of time, "it will not bring us down." But he said it's crucial to make payments on existing debt.

"When the United States government issued bonds, they said it had the full faith and credit of the United States, it didn't say the full faith and credit of the United States unless one political party is unhappy about some extraneous issue," said Buffett.

Related: Debt ceiling - countdown to default

Buffett said that despite the willingness of House Republicans to shut down the federal government earlier this week over Obamacare, he doesn't believe that they will do the same with the debt ceiling.

"That won't work long term. They'll discover it won't work long term, the public will turn on them and they'll have a counter-revelation," he said.

Related: Investors bet on a U.S. default

Buffett appeared with former Treasury Secretary Hank Paulson, who served in the Bush administration during the financial crisis five years ago. Paulson was also very critical of the House Republicans who let the government shut down. He said this current crisis is "self-inflicted," because "one element that does not reflect the views of the Republican party" has "hijacked the debate." But he also doesn't believe Congress will miss the debt ceiling deadline.

"These guys may threaten to take their mother hostage, but they'll never hurt their mother," Paulson said.