Amazon may eventually have 70 million banking customers

These are the companies Amazon owns
These are the companies Amazon owns

America could soon have a mega-competitor to its biggest banks: Amazon.

Amazon (AMZN) could wind up with more than 70 million banking customers over the next five years if it started to offer checking and other financial products, according to a recent report from management consulting giant Bain & Co.

To put that in context, that's about the same number of customers that Wells Fargo (WFC) currently has.

Is it realistic to think that Amazon could eventually have 70 million banking customers? Amazon hasn't even formally announced that it's looking to partner with big banks and offer its customers Amazon checking accounts.

But let's assume for a moment the Wall Street Journal report is true, and Amazon really is talking to JPMorgan Chase (JPM), Capital One (COF) and others about a banking partnership. Bain thinks Amazon could be onto something.

Bain surveyed nearly 135,000 consumers in 22 countries and found that more than half of the respondents in the US said they would buy a financial services product from a tech firm. Nearly three-quarters of the survey participants between the ages of 18 and 24 said they would buy a financial product from a tech company.

Amazon was named the most trusted tech company, followed by Apple (AAPL) and Google (GOOGL). (The survey was done in November, before the Wall Street Journal report.) That's noteworthy since a lot of these people, many of whom are still in school or looking for jobs, may not yet have established banking accounts just yet.

Related: Amazon wants to be your bank, too?

Maureen Burns, a Bain & Co. partner and leader in the firm's financial services practice, told CNNMoney that many college-aged consumers are currently more comfortable buying things with debit cards and cash.

But she thinks younger Millennials could be convinced to get an Amazon checking account since they trust the company, already use Amazon to buy things online or at Amazon-owned Whole Foods, and they watch Amazon shows and movies on Prime Instant Video.

She added that Amazon won't need to rely on extra (and annoying) consumer fees to make money since it won't have to spend much on actual bank locations, ATMs and workers. Who needs a teller when you can ask Alexa what your account balance is?

"Amazon may target younger customers that bigger banks haven't. With no branches, Amazon could go after younger customers and offer no fees or lower fees. They could also make transactions more seamless," she said.

Related: Amazon offers reduced Prime memberships to more low-income people

Burns said voice assistant devices like Amazon's Echo, Google's Home and Apple's new Siri-powered HomePod could be the key to getting many Millennials to open up accounts backed by tech firms. But she's still a little wary.

Although many customers now feel comfortable doing banking online or on their phone, not every tech innovation has worked out for banks.

"Online chat never took off," Burns conceded. "So it's not a given that voice assistant transactions will work out. But it could be easy for routine transactions like paying a bill."

Still, Burns said banks are now in a difficult spot. They need to work with Amazon and other tech giants. But they also have to be wary. She thinks Amazon is a much bigger threat to large financial services firms than younger fintech startup companies.

"Do banks need to be worried? I think they do. Amazon is aggressive in how they partner and getting a lot of the profits from deals," Burns said. "But you can't argue with the notion that banking customers have a digital need."

Perhaps CEO Jeff Bezos, who recently topped the Forbes list of the world's richest people with a net worth of more than $100 billion, will open an Amazon checking account?

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