More than 60% of millennials anticipate that they will be working during their retirement years (at least on a part-time basis), according to a recent study from CNBC. But it doesn't have to end up the way. If you are able to save some money over your working years and invest that into safe, blue-chip stocks that generate cash, that can make for a much more enjoyable retirement. Not only could you avoid working during these years -- you could also sit back and watch the money roll into your portfolio on a regular basis.

Three dividend stocks that can be pillars for your portfolio for the long term and generate significant cash are Walgreens Boots Alliance (WBA -0.61%)Fortis (FTS -0.10%), and Coca-Cola (KO -0.08%). They have strong track records of increasing dividend payments over the years, and they look like excellent investments to buy and hold.

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1. Walgreens Boots Alliance

Healthcare giant Walgreens raised its dividend in July, marking the 46th year in a row that it has bumped up its payouts to shareholders. Investors who hold the Dividend Aristocrat will now collect $1.91 per share every year, up from $1.87. With the increase, the stock is now yielding an impressive 4.1% -- well above the S&P 500 average of less than 1.4%. 

Investors have been wary of the company because of competition from online retailers like Amazon that are getting more involved in healthcare. There are even rumors that the tech giant may launch its own physical pharmacies. But Walgreens is no slouch, and it has been making moves to be more competitive as well. The company offers same-day prescription delivery from nearly all of its stores, every day. It is also working to open 600 primary care facilities over a four-year period in partnership with VillageMD.

Diversifying its business could help strengthen Walgreens's overall operations and make it a much better buy over the long term. It's already a trusted name and brand that that millions of Americans rely on. Close to 80% of the U.S. population lives within five miles of one of its drugstores.

While its profit margins have been slim (normally no higher than 4%), the company has posted a positive net income number in each of the past five years. And its payout ratio of 74% looks very sustainable. It may not be a top growth stock to buy, but the investment could be a great source of recurring cash flow. And the stock is cheap, trading at a forward price-to-earnings multiple of just 10; investors are paying 11 times future earnings for rival CVS Health.

2. Fortis

Utility company Fortis has been increasing its dividend payment for 47 straight years. Its yield of 3.7% is also above average and can provide investors with some long-term stability. Over the past four years, the company's profit margin has come in at 12% or higher. And the top line has been steadily growing during that time, too, from 8.3 billion Canadian dollars in 2017 to more than CA$8.9 billion in 2020 -- an increase of 8%. While that's not a whole lot of growth, utility stocks are known primarily for their safety rather than their growth potential

And safety is what you can expect with Fortis, which pays out less than 60% of its earnings to shareholders. That leaves plenty of room for the company to continue making further rate hikes and ensure that it eventually becomes a Dividend King. And for investors concerned about COVID-19, the good news is that management doesn't anticipate that the pandemic will have a "material financial impact in 2021."

The company expects that it will be able to increase its dividend by 6% annually at least until 2025. At the same time, it will still pursue growth opportunities, including a focus on cleaner energy -- Fortis plans to cut carbon emissions by 75% by 2035.

Whether you are a green investor or just want a great, reliable dividend to own, Fortis is a stock you should consider buying today.

3. Coca-Cola

Earlier this year, soft drink giant Coca-Cola announced it was boosting its dividend by 2.4%. At 59 years of consecutive increases, the stock has the longest streak of dividend hikes on this list. While it's a nominal $0.01 increase to $0.42, the dividend still pays a decent 2.9% annually. And if the company were to continue increasing its dividend payments by an average of 2.4% over the next two decades, its payouts would rise by 61%.

Although its payout ratio sits at over 100% due to the pandemic and some soft results, the future looks much stronger as the economy in many places has been opening back up. Per-share profit for the period ending July 2 was $0.61, which is well above its quarterly dividend and also 49% higher than the $0.41 profit it reported in the prior-year period.

Coca-Cola is a household name, and the business is a safe bet to remain profitable for the foreseeable future. While there might be short-term concerns about the stock amid rising case numbers of COVID-19, this is an easy stock for long-term investors to justify holding. The company has posted a profit margin of 22% over the trailing 12 months during what's been a very tumultuous period.