The Largest Bank in the US

By market value, Wells Fargo is now the largest bank in the US.  Even though it is a distant 4th in terms of assets and capital, WFC is the only mega-bank that trades at parity with its book value.  While WFC is a great bank, the relative valuation seems a bit off.  Under what economic scenario does Bank of America lose 71% of it's book value (as implied by its market cap) and WFC doesn't sustain any losses?

Wells Fargo Market Cap Chart by YCharts

Wells Fargo Total Assets Chart by YCharts

Wells Fargo Shareholders Equity Chart by YCharts