How can a bank lose $2 billion in six weeks?

That's just one of the mysteries surrounding the news that JPMorgan Chase, widely thought one of the safest U.S. banks, is gushing red ink from bad trading bets. As details slowly emerged Friday, the shares of the nation's largest bank fell hard, as did those of several rivals.

The story behind the loss is complex, and rich in irony. How it's viewed could influence regulators implement a major financial overhaul law called Dodd-Frank. How hard regulators crack down on bank could have a big impact on the stability of the financial system.

Here are answers to some questions about the loss:

Q: How exactly did the bank lose so much so fast?

A: First, start with the irony. JPMorgan says the losses came from a trading portfolio designed to offset losses in the bank's lending business. Instead of offsetting losses, these so-called "hedges" added to them.

JPMorgan extends money to companies through loans and by buying bonds. The bank was worried that it might not get all its money back, so it bought protection. Though it didn't detail how it did this, banks typically buy credit default swaps, essentially insurance contracts that pay out when companies stiff their lenders.

It gets more complex. In the often dizzying, Alice-in-Wonderland world of banking, these hedges are themselves sometimes hedged, and that's exactly what JPMorgan did. The bank apparently thought it had bought too much protection, so it hedged its hedge.

It's that second hedge, basically a bet that companies would pay back their loans, that led to the losses.

Q: How does the "London Whale" figure into the story?

A: News reports before the bank announced its loss said that a trader at the bank dubbed the "London Whale" had invested heavily in an index of credit-default swaps, and that the bets were producing losses. But in a conference call Thursday, Jamie Dimon, the CEO of JPMorgan, said the news reports about London trades were only "somewhat related" to the losses. He provided no other details.

Q: Why are other bank stocks falling on the news?

A: It's not just the size of the bet that's scaring investors, but its complexity. The fact is, not even experts know how precisely big banks make money, and occasionally lose it. Their wagers are largely hidden. The opaqueness, which investors normally shrug off, is spooking them now.

Investors are uneasy also because JPMorgan has a reputation of managing risks better than almost anyone in the business. Investors seem to be asking: If this bank can lose $2 billion in six weeks, maybe others can, too?

Finally, there's the regulatory threat. The loss comes amid heated debate in Washington over just how tightly to regulate banks. "The timing of the JPMorgan announcement couldn't be worse," said Whitney Tilson, head of hedge fund T2 Partners, speaking at an industry gathering in Las Vegas.

Investors fear that bank profits could be pinched by the so-called Volcker Rule restricting trading that banks do with their own money, as opposed to clients' funds. Dimon has been an outspoken critic of the rule, and an impactful one given his skill at navigating his bank in recent years. JPMorgan was the only bank to remain profitable during the 2008 financial crisis.

Now that Dimon has been pushed off his pedestal, investors are worried that regulators will be tougher in enforcing the new rule.

Q: Isn't the trading that led to the loss banned already?

A: No. The rule doesn't take effect until July, and even then regulators are suggesting banks will have another two years to comply.

In any case, it's not clear that the trade in question were subject to the rule. In the conference call Thursday, Dimon said the trades that backfired were hedges, not bets for profit, so they wouldn't have fallen under the rule.

But some experts have doubts.

Nancy Bush, a banking analyst at NAB Research, says it's not always clear what is hedging and what is gambling. The size of JPMorgan's loss makes her suspicious.

"So they made money on hedges and then they hedged some more," she said. "At some point it goes from being a hedge to being a money maker. They crossed the line here somewhere and it's going to cost them."

Sen. Carl Levin from Michigan, the chair of a subcommittee that investigated the crisis, put it more bluntly. "This is not a hedge," he said. He called the loss a "stark warning" about the danger of "risky bets" at banks.

Q: How much will the trading loss hurt JPMorgan?

A: Likely not much at all, putting aside the impact of tougher regulation. JPMorgan is a big money maker. The $2 billion loss, which is before accounting for taxes, compares with $19 billion in net income last year and $16 billion the year before that.

What's more, Dimon said that $2 billion loss will be offset by $1 billion trading bets that have already paid off. Dimon said there are $7 billion more paper gains from trades that he can tap in case losses grow.

Q: Are more losses possible?

A: Dimon said he is trying to unwind the bad bets in a "responsible" manner to minimize losses, but prices can move against him. That would mean more losses. Dimon has said the $2 billion could become $3 billion depending on how markets react.

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AP Business Writers Pallavi Gogoi in New York, Daniel Wagner in Washington and Christina Rexrode in Las Vegas contributed to this report.