多年以来，摩根大通（JPMorgan Chase）这家世界上最冒险的银行每每总能涉险过关。当然，一路上小麻烦不断。但基本上，投资者对于这家由杰米•戴蒙领导的银行总是能放手不管。次贷问题：过去你们已经证明，你们能应付。止赎问题：我们坚信你们已安排了最好的人手。相当于印度GDP的衍生品投资组合：我们相信你们掌握着足够的资金。

    事实上，尽管摩根大通拥有如此庞大的规模、复杂性和风险，但投资者们允许戴蒙和摩根大通以华尔街最低的资本缓冲（即可抵御损失的权益资本）一路“前行”。如果对摩根大通的贷款和投资按风险进行分类（这种分类虽不可靠但仍被华尔街采用），该行的资本充足率仅为10%。而花旗（Citigroup）、高盛（Goldman Sachs）分别为13%和15%。

    不过，这样的差距似乎并没有让投资者感到不安。摩根大通的股票估值一度居华尔街前列。直到最近，它还是少数几家市净率高于1的大银行之一。这意味着华尔街认为，该公司实际价值超出其账面价值。花旗目前的市净率仅为0.5倍。

    然而，上周，这一切全都变了。上周四下午，戴蒙通过一个紧急电话会议告诉分析师们，过去40天摩根大通首席投资办公室在一场交易中损失了20亿美元；该部门原本应通过投资，降低该行风险，而不是加剧风险。上周五，摩根大通股价狂跌近10%，收盘价不到37美元。

    有些人只看这20亿美元损失，认为对于通常每季盈利50亿美元并拥有550亿美元现金的一家银行来说，算不了什么。毫无疑问，摩根大通能处理好这事。事实上，考虑到该部门所从事的所有其他交易，该部门合计损失降至8亿美元。整体而言，该行这个季度看起来仍然有望获得高额利润。

    但实际损失将远远超出这些。首先，摩根大通在这场交易中的最终损失可能超出已经披露的金额。有报道称，这项让摩根大通陷入麻烦的交易规模可能高达1,000亿美元，主要由英国一名外号“伦敦鲸”的交易员操盘。摩根大通绝不会损失1,000亿美元那么多。但像摩根大通这样对某一指数进行多倍押注的交易可能需要付出昂贵的代价才能解除，必须与信用度高的大公司进行交易。戴蒙在分析师电话会议上表示，该行在这项交易上的损失可能会进一步扩大，但他没有透露具体数字。

    For years, JPMorgan Chase (JPM), perhaps the riskiest bank in the world, got a pass. Sure there were minor hiccups along the way. But basically investors had the attitude with the bank run by Jamie Dimon that they were going to be hands off. Sub-prime mortgage loans: You've proved you can handle them. Foreclosure problems: We're sure you've got your best people on it. A derivative portfolio roughly the size of the GDP of India: We trust that you have covered your bets.

    In fact, despite its huge size and complexity and risk, investors have allowed Dimon and JPMorgan to skate by on one of the smallest capital cushions, which is how much equity you have to protect against losses, on Wall Street. When you sort JPMorgan's loans and investments by riskiness, a dubious calculation, but used by Wall Street nonetheless, the bank holds an equivalent of just 10% of that as capital. That compares to 13% at Citigroup (C) and 15% at Goldman Sachs (GS).

    That shortfall, though, didn't seem to bother investors. JPMorgan's shares were rewarded with one of the richest valuations on Wall Street. Until recently, it was one of the few big banks to trade above book value, meaning Wall Street believed it was worth what it said. Citigroup's shares trade at a price-to-book of 0.5.

    This week, all that changed. On Thursday afternoon, Dimon told analysts in an emergency conference call that JPMorgan's chief investment office, a division that is supposed to place investments that lower the risk of the bank, not increase it, had lost $2 billion on a trading strategy in the past 40 days. JPMorgan's shares fell nearly 10% on Friday and closed at just under $37.

    Some have focused just on the $2 billion loss, commenting that it's not that big a deal for a bank that has typically been earning $5 billion every three months and has $55 billion in cash. There's no question JPMorgan can handle it. In fact, factor in all of the division's other trades, and the bank's loss from the division shrinks to $800 million. Overall, the bank will still likely show a hefty profit this quarter.

    But the actual cost of the loss will be much bigger than that. First of all, JPMorgan could end up losing more on the bet than it has already disclosed. Others have reported that the trade that got JPMorgan into trouble, which is mostly attributed to a single trader who is based in the UK and has come to be known as the London Whale, could be as large as $100 billion. The bank won't lose anywhere close to that. But transactions like the one JPMorgan appears to have, where it makes multiple bets involving a particular index, in this case one that has to do with large, credit-worthy companies, can be very costly to unwind. Dimon on the conference call with analysts said the bank's losses on the trade are likely to increase but he didn't say how much.