Everyone knows that a small handful of banks are too big to fail. But just how big are they?

Data released earlier this week helps to paint this picture. According to the FDIC's summary of deposits, the 10 biggest banks hold almost half of the nation's $9.4 trillion in deposits.

Bank of America (NYSE:BAC) topped the list for the 15th consecutive year since its seminal merger with Nationsbank in 1998. At the end of the second quarter, it was the only bank with more than $1 trillion in total deposits, equating to a national market share of 12.2%.

It's followed in quick succession by Wells Fargo (NYSE:WFC) and JPMorgan Chase (NYSE:JPM), with market shares of 10.3% and 10.1%, respectively.

And following a marked jump down, Citigroup (NYSE:C) handily outpaces a bevy of regional banks headed by U.S. Bancorp (NYSE:USB). Citigroup, which recorded the second largest year-over-year increase in deposits, finished the second quarter with a 4.7% nationwide market share while U.S. Bancorp's stayed relatively consistent at 2.5%.