Historically, dividends are the X-factor that can supercharge the returns of an investment portfolio.

In 2013, Bank of America/Merrill Lynch released a report analyzing the performance of companies that initiated and grew their dividends over a 40-year period between 1972 and 2012. BofA/Merrill Lynch then compared this return to that of non-dividend-paying stocks over the same time frame. The result was a 9.5% average annual return for the dividend stocks, compared to a 1.6% average annual return for the non-dividend stocks.

To put these figures into an easier-to-understand context, imagine you had $1,000 to invest back in 1972. Had you put that $1,000 into an assortment of non-dividend stocks, you'd have about $1,900 by 2012. By comparison, this same $1,000 invested into companies that initiated and grew their payout over 40 years would be worth roughly $38,000!

Of course, not all dividend stocks are created equal. While the following four stocks may not all be known for their flashy yields, they have the luxury of being the stock market's biggest dividend payers.

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Microsoft: $15.46 billion

Here's an interesting stat to run by your friends: Even though software-giant Microsoft (MSFT 0.45%) has a sub-1% yield, it possesses the largest payout on Wall Street. With close to 7.6 billion shares outstanding and a $2.04 base annual payout, Microsoft is doling out almost $15.5 billion a year to its shareholders.

Perhaps the scariest thing about Microsoft's robust dividend is that it's really just a drop in the bucket. Microsoft ended its fiscal third quarter with $136.5 billion in cash, cash equivalents, and short-term investments, compared to $63.3 billion in combined short- and long-term debt. In a typical year, Microsoft's operating cash flow is going to easily top $50 billion. As I said, a nearly $15.5 billion dividend payout each year is no sweat whatsoever for one of the few remaining AAA-rated public companies.

Microsoft's success is predominantly tied to its cloud-service investments, as well as its dominant position among PCs in the consumer and enterprise ecosystem. In the latest quarter, which I remind you was marred by unprecedented economic disruption tied to the coronavirus pandemic, constant-currency sales for Azure soared 50% from the prior-year period, with other cloud service segments tied to core brands like Office, Windows, and Dynamics showing constant-currency sales growth of between 7% and 15%. 

Suffice it to say that Microsoft's payout is about as rock solid as they come.

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AT&T: $14.83 billion

On the other hand, there's telecom-behemoth AT&T (T 0.29%), which is a relatively slow-growing company with a flashy dividend. AT&T is currently riding a 36-year streak of increasing its annual dividend and yielding an eye-popping 7%. This means income seekers who choose to reinvest their payouts from AT&T should be able to double their money from dividends alone about once a decade.

AT&T is able to pay more than $14.8 billion in dividends each year due to the high predictability of its cash flow. There's not a whole lot of churn for AT&T's wireless business, and while the company has been a victim of cord-cutting in recent years -- AT&T owns satellite TV operator DirecTV -- it hasn't made much of a difference in operating cash flow, due to growth in other segments.

AT&T looks like a good bet to keep its dividend streak alive for years to come, especially with the rollout of 5G networks, which really kicked into high gear this year. Upgrading wireless infrastructure won't happen overnight or be cheap, but it'll lead to a multiyear technology-upgrade cycle for consumers and businesses that should drive up data consumption. Since data is the cornerstone of AT&T's wireless margins, this is a good thing.

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ExxonMobil: $14.72 billion

Despite all the issues oil stocks have contended with in 2020, including a brief period of negative crude prices, integrated oil and gas player ExxonMobil (XOM 1.26%) stands tall with the third-largest payout on Wall Street at $14.7 billion.

ExxonMobil is also a Dividend Aristocrat, as the company increased its payout in each of the past 37 years. It also has one of the highest yields -- 8% -- you'll find among large-cap or megacap stocks. Income seekers who reinvest their payouts from ExxonMobil could double their money in about nine years. Of course, this all depends on the company continuing its payout, which will, in turn, depend on the outlook for crude demand.

ExxonMobil benefits from being an integrated company, which is a big reason it's been able to hold firm on its dividend as other oil patch players slash or suspend their payouts. The company's downstream refining and chemical operations are able to step up during periods of crude-pricing weakness and offset some of the lost cash flow tied to the drilling and exploration side of the equation.

Likewise, ExxonMobil has the ability to slash its capital expenditures to reduce outlays and preserve its dividend. For now, this payout remains safe.

Apple employees straightening Apple Watch band displays.

Image source: Apple.

Apple: $14.2 billion

Finally, it's that "fruit company" everyone's come to know and love, Apple (AAPL -0.60%). Had Apple not so aggressively repurchased its own stock in recent years, it would probably top this list by a few billion dollars. But since its share count has been reduced through buybacks, it's "only" paying out $14.2 billion in dividends each year.

Similar to Microsoft and AT&T, there's simply no concern about Apple making good on its dividend commitments. Apple has $94 billion in cash and marketable securities that it can easily access and was able to generate a whopping $75.4 billion in operating cash flow over the trailing 12-month period. Apple is a money machine, and this $14.2 billion payout is hardly worth raising an eyebrow over for CEO Tim Cook and the company's board of directors.

What makes Apple tick is its combination of brand appeal and innovation. Consumers will seemingly line up around the block to get their hands on the company's latest smartphone and other devices. This cult-like following, combined with Tim Cook's desire to see Apple transform into a wearables and services model, is what'll keep the growth needle pointed in the right direction.