While we're only halfway through the trading day, traders have already been on a veritable roller coaster. The Dow Jones Industrial Average (^DJI -1.56%) began the morning higher following positive economic news out of China, then dove into negative territory after downbeat news was released about Apple (AAPL -0.43%), and has since recovered courtesy of the financial sector.

A new report by market researcher IDC estimates that Apple's share of the global tablet market is bound to fall. More specifically, IDC estimates that its share will slip to less than half by 2016, down from 56.3% today. The reason? Increased competition from the likes of Microsoft (MSFT -4.11%) and Google (GOOGL -2.19%), both of which have recently released tablets of their own. Shares in the Cupertino-based company are down 4.6% on the news.

Shares of Netflix (NFLX 0.47%) are also down today after rallying sharply at the end of trading yesterday. The impetus for yesterday's rally was the company's announcement that it had inked a deal with Disney (DIS -1.86%) for exclusive rights to the latter's movies. According to Bloomberg News, under the terms of the blockbuster deal, Netflix will get immediate access to classic videos like Alice in Wonderland. Next year it will then have access to direct-to-video titles. And starting in 2016, it will begin streaming new titles. Needless to say, this is a major coup for the recently struggling company.

Also making waves today, shares of Citigroup (C -1.47%) are up sharply after the nation's fourth-largest bank by assets announced its decision to slash 11,000 jobs and $1.1 billion in annual costs. According to Citigroup's new CEO, Michael Corbat:

These actions are logical next steps in Citi's transformation. While we are committed to -- and our strategy continues to leverage -- our unparalleled global network and footprint, we have identified areas and products where our scale does not provide for meaningful returns. And we will further increase our operating efficiency by reducing excess capacity and expenses, whether they center on technology, real estate or simplifying our operations.

The move comes on the heels of a disappointing hird quarter in which the bank recorded a $4.7 billion charge-off related to the ongoing sale of its brokerage unit, Morgan Stanley Smith Barney. The charge-off was ultimately the last straw for the board of directors, which effectively fired Vikram Pandit, the lender's former CEO, following the quarterly conference call.

Many investors sees today's announcement as a step in the right direction. David Tepper of hedge fund Appaloosa Management, a major investor in Citigroup, said, "We think they are rationalizing the business in an intelligent way." The reason for this can be seen in the chart below, which provides a comparison of Citigroup's efficiency ratio (noninterest expense divided by revenue before loan losses) to its peers JPMorgan Chase (JPM -0.02%), Bank of America (BAC -1.63%), Wells Fargo (WFC -0.57%), and US Bancorp (USB -1.73%).

Source: S&P Capital IQ.

As you can see, by this measure, Citigroup is currently the least efficient too-big-to-fail lender of the bunch, with an efficiency ratio of 89% compared to B of A's 78% and JPMorgan's 60%, among others. In effect, this means that it costs Citigroup $0.89 to make $1. A more reasonable figure is somewhere between 45% and 60%.

Shares in B of A, which had previously implemented a similar program known as "Project New BAC" much earlier, are also up considerably on the news, cresting the $10 mark for one of the first times this year. And while JPMorgan temporarily dipped into negative territory in midmorning trading, it has since rallied sharply and is up 1.3% at the time of writing.