S&P 500, Dow drop as big banks fall after results
- JPMorgan dips despite posting jump in profit.
- Citigroup, Wells Fargo slip after results.
- Walmart drops as head of e-commerce to retire.
- Retail sales fall again in December.
- Indexes: Dow down 0.36%, S&P slips 0.26%, Nasdaq up 0.12%.