I can't tell you how many times I've called one bank or another "the nation's second (or third, or whatever) largest bank by assets" to help put the bank I'm writing about into context. After doing this countless times, however, I figured that what would really help from a contextual standpoint is a chart. What follows, in turn, is a graph of the nation's largest lenders -- all but one of which has assets in excess of $20 billion.

Source: Standard & Poor's Capital IQ.

While it's not obvious from the chart, you can separate these institutions into three different buckets. The first bucket concerns the most widely discussed too-big-to-fail banks: JPMorgan Chase, Bank of America, Citigroup, and Wells Fargo. Then comes the unofficial too-big-to-fail lenders (those with assets in excess of $50 billion and thus subject to the Federal Reserve's more stringent stress test process). This group contains U.S. Bank (USB -0.84%), PNC Financial (PNC -1.44%), and BB&T Bank (TFC -1.50%), among others. And the final group encompasses lesser-known banks like First Niagara Financial (NASDAQ: FNFG) and People's United Financial (PBCT) with between $20 billion and $50 billion in assets.

For those of you interested in bank stocks, I encourage you to use this list to consider diversifying your holdings from those institutions at the top of the list to some closer to the bottom. As I discussed here, it's at the bottom where you'll often find the best returns.