In just two years, Apple Inc's (AAPL -2.54%) debt has jumped from $0 to $47 billion, making it one of the biggest borrowers on Wall Street. While the company has invested alongside its debt to establish a seemingly conservative position, taking on $15 billion or more of debt annually may not be sustainable. 

Here are few of the challenges Apple faces in its quest to return capital to shareholders. 

The next billion-dollar iSecret
The world's biggest tech company forgot to show you something at its recent event, but a few Wall Street analysts and the Fool didn't miss a beat: There's a small company that's powering their brand-new gadgets and the coming revolution in technology. And we think its stock price has nearly unlimited room to run for early, in-the-know investors! To be one of them, just click here.