STOCKS SLIP: Here's what you need to know

Stocks had their biggest drop in two weeks on another relatively quiet day on Wall Street. 
First, the scoreboard:
Dow: 18,552.02, -84.03, (-0.45%)
S&P 500: 2,178.15, -12.00, (-0.55%)
Nasdaq: 5,227.11, -34.90, (-0.66%)
WTI crude oil: $46.58, -$0.84, (+1.84%)
Aetna dealt Obamacare another major blow. The giant health insurer announced on Monday that it would be pulling out of nearly 70% of the counties in which it offers coverage under the Affordable Care Act. The com