What does $24 billion mean to you? Exactly, it blows my mind, too. That's why it's so crazy that Citigroup (NYSE: C) is expected to write off $24 billion tomorrow when it announces its fourth-quarter earnings.

In this wild financial fracas we've come to know and love, the numbers just keep getting bigger and bigger, and investors seem to continue acclimatizing themselves to ever higher mountains of losses. Eh, $24 billion? At least it wasn't $100 billion or $1 trillion.

In fact, with reports circulating today that Citi may be writing off that sizable chunk -- not to mention laying off 20,000 employees -- the stock is actually up a bit as I write this. It shouldn't be all that surprising, though, given the beating that Citi's stock has already taken and the fact that Merrill Lynch (NYSE: MER) and its new CEO, John Thain, have done a great job breaking the ice for it. After all, if Merrill, which is currently valued at about a third of Citi, can be expected to absorb $15 billion in writedowns in one quarter, why couldn't Citi tackle $24 billion?

In truth, investors are likely reacting to two forces -- similar to the rumored losses at Merrill. First, Vik Pandit, Citi's new CEO, wants to start off on the right foot, and that doesn't mean being overly optimistic about the company's current position and taking a "glass half full" view of potential losses. Along with that, investors can start getting a better idea of what Citi is really worth now that the big losses are coming to light. The stock has been cut in half from its 52-week high, and that means investors have already cut nearly $150 billion off the company's valuation.

Of course this only works out if there's not another kitchen sink hiding somewhere at Citi and Merrill. At this point, it's difficult for any investor to gauge what magnitude of losses is really possible. Given the size and complexity of a Citi, Merrill, Bear (NYSE: BSC), or Goldman (NYSE: GS), coming up with a valuation in good times can be difficult. Right now, it's darn near impossible, and so these stocks are largely bets on the ability of management, on a relatively optimistic macroeconomic outcome, and that the sins of the past few years aren't even worse than imagined.

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Fool contributor Matt Koppenheffer does not own shares of any of the companies mentioned. The Fool's disclosure policy has never once been caught with its pants down. Of course, it doesn't actually wear pants.