I was blown away by a recent visit with Citigroup CEO Mike Corbat

Source: Citigroup

Citi’s new global headquarters features open office space that allows for easier interaction between colleagues and is designed to promote communication across teams and functions.

I started my career in investment banking in 1997, following the path of least resistance from the Ivy League to Wall Street. Though the work was interesting and exciting, I knew I wasn't in it for the long haul. I looked at executives 10 years my senior and realized the life I wanted for myself was very different; I wanted something that the banking industry couldn't offer. At least, not back then.

I recently connected with Mike Corbat, chief executive officer of Citigroup – an institution with 204-year-old roots in the finance industry. When you think old-school banking, you think big marble and walnut monoliths with suspender-wearing financiers and corner offices with skyline views. You think Gordon Gekko, smoke-filled trading floors and workaholics. While some of these stereotypes have gone out of style (offices are now nonsmoking, and no one really wears suspenders), there remain a few preconceived notions about the finance industry. Which is why, on my visit to meet with Mike at Citigroup's New York offices, I was totally blown away.

Open spaces with bright, clean lines. No corner offices. No doors, even. This couldn't possibly be a bank; it looked more like Zillow Group's dotcom-esque headquarters in Seattle. The space, Mike explained, was meant to embody what the company stands for: removing friction from its customers' everyday lives. As a global business whose No. 1 need is speed to decision, Mike's job as CEO is to make that ever easier for employees. Doors are friction, he explained; they delay decision-making by tying up deliverables, untouchable on someone's desk. Mike passionately explained that a company's physical space should reinforce the company's cultural values. He sounded more like a start-up CEO than the CEO of a company with a $130 billion market cap.

Source: Zillow Group

Zillow Group’s headquarters in downtown Seattle.

The office was just the tip of the iceberg in Citigroup's radical redefining of an institution. In an industry that has historically been inherently mercenary, Mike and his leadership team have found a way to attract individuals seeking more than just a paycheck and power – the mission-driven millennials over whom all companies fret, puzzled by how to motivate and retain them. Through Citigroup's campus hiring programs alone, the company hires more than 3,000 recent college graduates every year. Mike and his team get that millennials want fulfillment professionally and personally, and they expect both from their employer. "Today with millennials, if you're not educating, challenging and stimulating them, they're up and gone," says Mike in the latest Office Hours podcast. Programs like gap years in Africa working in microfinance help Citigroup retain talent while also giving employees opportunities for growth around the company's mission of giving back to the world.

In recent years, Wall Street has lost millennial talent to tech start-ups touting missions and rapid career progression; the traditional, prescribed path of investment banking appeals less and less to this group. More financial institutions need to follow Citi's lead if they are going to keep pace with the tech industry's stiff competition, not just with workspace and career planning but also with values that resonate with millennials, like work-life balance.

In talking with Mike, I realized that he has solved one of the challenges I've struggled with as Zillow Group has gotten ever larger: Scaling the CEO role as employee count grows. I've always taken a very hands-on approach to management, but with over 2,500 employees it is now impossible to be involved with every single employee. Mike has over 220,000 employees at Citigroup in more than 160 countries and jurisdictions.

Michael Corbat, chief executive officer of Citigroup Inc.

Mike's key to scaling his capacity to care for all employees and help them personally identify with the organization lies in ethics and culture. People need a sense of belonging to a company and an understanding of how their day-to-day work feeds into a mission. To be thought of as individuals, they need to feel as such. They need all this to have a sense of pride — it's essential to caring about a company, feeling invested in it and responsible for its success.

I've shared with my colleagues at Zillow Group one of my biggest fears as we grow: that we lose our culture of ownership, our commitment to our mission and our individual and collective investment in our success. According to Mike, these attributes can scale as long as you make the experience personal, as long as you help people feel like individuals.

After my talk with Mike, I wondered: If Citigroup had been in the 1990s what it is today, would I have stayed in investment banking? I guess we'll never know. In the meantime though, my conversation with Mike about leadership and corporate culture will make me a better CEO at Zillow Group.

Commentary by Spencer Rascoff, chief executive officer of Zillow Group, which houses a portfolio of real-estate sites, including Zillow and Trulia. He is also the co-author of "Zillow Talk: The New Rules of Real Estate." Follow him on Twitter @spencerrascoff.

You can listen to the full episode of Rascoff's "Office Hours" podcast with Mike Corbat or read the transcript here.

For more insight from CNBC contributors, follow @CNBCopinion on Twitter.