Amazon's 2017 annual 10(K) federal financial filing reported $4.1 billion in net operating income. But the profit was entirely attributable to Amazon's tech infrastructure line of business, Amazon Web Services (AWS). Amazon's retail sales business reported a loss.

Unless you're a professional securities analyst or MBA, it may not be easy to discern that Amazon lost money on its main business from the company's required 10(K) annual public disclosure filing with the U.S. Securities and Exchange Commission. But it's disclosed in this table on page 69 of Amazon's 10(K) for 2017. AWS earned a $4.3 billion profit on $17.5 in net sales revenue, while total profits were $4.1 billion on well over $100 billion of sales.

Amazon could afford to take a loss on its retail business. It's a long-term investment in gaining market share. Losses taken on dominating internet retailing were offset by AWS, Amazon's business of building the infrastructure of the web, which has been very profitable.