McKesson (MCK 1.27%) could be the largest company you've never heard of. Its annual sales surpass $273 billion, dwarfing household brands like Target, Nike, and The Home Depot.

The company is a hidden but vital cog in the healthcare industry, generating robust returns for investors. A $10,000 investment at its initial public offering would be worth more than $612,000 today.

The company has spent years building its dividend track record. Management has raised its payout to shareholders for 15 consecutive years.

McKesson has excellent financials, growth, and a competitive moat to become one of the next great dividend stocks. Here is why investors should consider it for any long-term dividend portfolio.

The hidden titan of healthcare

McKesson helps healthcare providers lower costs and operate more efficiently. It distributes pharmaceuticals and medical supplies, and it provides technology services.

Healthcare, especially in the United States, is a complex business with many moving parts. You can think of McKesson as a behind-the-scenes middleman that helps bring products and services to patients.

Most of McKesson's business is concentrated in its U.S. pharmaceutical distribution business, contributing over 80% of its total revenue. Pharmacies are very competitive. They typically sell prescription drugs at thin margins, making their money on general food and merchandise sales as patients visit their stores.

McKesson's massive size makes it hard for competitors to undercut it on pricing. The company's operating margin is just 1.5%, meaning it brings in less than $0.02 in operating profit on every sales dollar.

MCK Revenue (TTM) Chart
Data by YCharts. TTM = trailing 12 months.

But since McKesson does more than $250 billion in revenue, those pennies add up to billions of dollars in free cash flow. This economy of scale is similar to how Walmart can continually sell products at lower prices than competitors.

McKesson isn't the only game in town; it competes with Cardinal Health. But the former has been able to grow revenue by 125% over the past decade, and cash profits have mostly kept up, growing 101%.

The dividend has plenty of room for growth

McKesson isn't exactly new to the dividend game. Management had frozen its dividend for several years before beginning a growth streak that has hit 15 years. And there don't seem to be any obstacles to decades of potential dividend growth.

The company has raised the dividend by an average of 10.5% annually for the past five years. Sure, the starting dividend yield of 0.6% at today's share price isn't anything to get excited about. But your dividend will double every seven years at the rate it has issued increases, which can mean substantial growth over the long term.

MCK Dividend Chart
Data by YCharts.

McKesson might have one of the lowest dividend payout ratios, at just 7% of its cash flow. Considering that cash flow doubled over the past decade, the company could raise the payout by double digits each year and still have a ton of financial slack in the payout ratio because it's starting from such a low point.

Is the stock a buy today?

A low dividend yield means investors want more from the stock than passive income. McKesson could have you covered there, too, since analysts believe the company could grow earnings per share (EPS) by an average of 10% annually over the next several years.

The stock trades at a price-to-earnings (P/E) ratio of just 14 against a median P/E of 24 over the past 10 years. McKesson's growth outlook is similar to the S&P 500's long-term growth rate, yet the stock trades at a cheaper P/E (nearly 18). That could give investors a margin of safety, with the potential for upside if the market turns bullish.

McKesson could be a great addition to any long-term portfolio; its growth outlook and valuation seemingly tee up double-digit investment returns, and that dividend has enough powder in the keg to someday become a household name among dividend investors.