Citigroup's ( C ) total assets increased 1.1% to $1.353 trillion, 9% of the total. The biggest of the big, JPMorgan Chase ( JPM ), gained 1.6% in total assets to $2.105 trillion, 14% of the total. Wells Fargo's ( WFC ) total assets increased by 3.6% in the second quarter to $1.436 trillion, 10% of the total. Even with improved balance sheets these banks still face economic hurdles. Here's why: Reduced Mortgage Activities. The big banks have been cutting their mortgage activities and this contributed to a $3.6 billion year-over-year decline in noninterest income. Trading Income has been declining for four consecutive quarters down by $721 million, or 10%. Exposures to Notional Amount of Derivatives. The seven largest banks control 98% of the $239.2 trillion in notional amounts of derivative contracts. Assessments for the Deposit Insurance Fund. The bigger banks face larger assessments than the smaller banks. The DIF balance rose to $51.1 billion at the end of the second quarter.