It starts with a solid business plan and a relentless focus on executing that plan well. We refine our plans on a regular basis to ensure our company is well positioned to meet the needs of our customers and take advantage of opportunities that may exist in the market. We also foster a culture that encourages employees to maintain focus on execution every day by delivering on our service commitments to our policyholders.
The steps we've taken to diversify our business and take a more disciplined approach to pricing and underwriting have served us well. A decade ago, our business was heavily focused in the disability and life markets. Today, group disability accounts for less than a third of our business. A full 31 percent of our 2012 earnings came from voluntary benefits through our Colonial Life and Unum US businesses. Our focus on geographic and product diversity have helped us become a more versatile benefits provider for our customers and have better positioned us for any economic environment.
In addition to growth in voluntary benefits, we've seen positive trends in other markets we have targeted for growth, such as our Unum US core market (under 2,000 lives cases) and our Unum UK group income protection business. In 2012, premium income in these markets increased nearly five percent.
This growth has not come at the cost of sound business principles — or our customer service. We apply rigorous underwriting and expense management practices to ensure we minimize risk for our customers and our shareholders, and continue to improve the way we do business. As a result of our disciplined underwriting, for instance, we've seen our benefit ratios decline or remain stable over the past seven years for Unum US and Colonial Life. And our expense ratios have improved over the last three years as we've analyzed our operations to find ways to work smarter. All the while, our already high customer satisfaction scores have continued to climb even higher as we consistently deliver the quality service that customers expect from us.
By consistently executing on our operating plan, we delivered on our commitments to shareholders too. With 2012's operating earnings per share growth of 5.7 percent, we capped seven consecutive years of operating EPS growth. Return on equity for 2012 was also a solid 12.3 percent, a key indicator that our business continues to deliver value for our investors.