BB&T (TFC -1.67%) and SunTrust Banks (STI) announced today that they're teaming up, merging into a new company to form the sixth-largest bank in the United States. Here are three key facts investors should know now.

1. It's a true merger of equals

These super-regional banks operate in many of the same markets in the southeastern U.S. and up the eastern coast. SunTrust will technically merge into BB&T, with shareholders of BB&T owning 57% of the combined company and SunTrust shareholders owning the other 43%.

Atlanta skyline at dusk.

Image source: Getty Images.

BB&T will issue 1.295 shares of stock for each share of SunTrust outstanding. The combined company will have a new name, which wasn't identified, and house its corporate offices in Charlotte, North Carolina, roughly halfway between Atlanta, Georgia (SunTrust's headquarters), and Winston-Salem, North Carolina (BB&T's headquarters).

The deal is immediately accretive for BB&T shareholders, as its shares trade at a higher multiple of tangible book value than SunTrust's. In a presentation, BB&T said it expects tangible book value per share to increase by 6% after one-time deal expenses, provided the merger closes as expected in the fourth quarter of 2019.

2. Cost cuts are key

As with most bank mergers, this one has its roots in geographic overlap. BB&T and SunTrust both operate in the southeast United States, with branch networks that cross paths in most major southern cities.

In the image below, BB&T branches are blue; SunTrust's are red.

Map of BB&T and SunTrust branches. BB&T branches are blue; SunTrust's are red.

Data source: FDIC as of June 2018. Map by author using Google Maps.

When the two banks are combined, one should expect branch closures to follow. In a presentation detailing the deal, the banks said they have identified 740 branches within 2 miles of one another. In Cary, North Carolina, for example, BB&T and SunTrust have branches on opposite sides of a street corner. (Amusingly, a Bank of America branch sits between them.)

The banks didn't specifically mention how many branches would be consolidated, but a target of $1.6 billion in annual expense savings suggests hundreds of closures are likely.

Check out the latest BB&T and SunTrust earnings call transcripts.

3. It's the largest deal since the financial crisis

On their own, BB&T and SunTrust sit just below the $250-billion-in-assets threshold at which a bank becomes a systemically important financial institution, or "SIFI" bank. When combined, the two will have roughly $442 billion in assets, $301 billion in loans, and $324 billion in deposits.

Big bank deals have been nonexistent since the end of the financial crisis. Investors may remember M&T Bank's long-delayed acquisition of Hudson City Bancorp, which stalled for more than three years in regulatory limbo. That deal finally closed in 2015.

A friendlier regulatory environment should bode well for BB&T and SunTrust, which will cross the SIFI threshold in grand fashion, combining to become the sixth-largest bank by assets.