But in recent months, Mr. Bloomberg — who still owns 88 percent of the company — has become an increasing presence at Bloomberg's Lexington Avenue headquarters. Those "few hours" soon turned into six and seven hours a day with Mr. Bloomberg taking a hands-on role in meetings and strategy decisions. Mr. Doctoroff, a former deputy mayor of New York and private equity executive, told Mr. Bloomberg about two weeks ago that he planned to resign, frustrated with how the leadership dynamic had shifted with Mr. Bloomberg back in the building. Mr. Bloomberg urged him to stay and remain chief executive, but Mr. Doctoroff demurred.
"This wasn't the plan," said Mr. Bloomberg, sitting next to Mr. Doctoroff on Wednesday at a coffee shop on the Upper East Side. "It was his idea. If it was up to me, he would have stayed."
Mr. Bloomberg said he fell in love again with the company that he founded in 1981. He said that after vacationing for a couple of weeks in January and working on his philanthropy, he realized that he felt most excited by his work at Bloomberg L.P.
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He will take charge of a company that is significantly bigger and more powerful than the one he left more than a decade ago, but it also perhaps faces more challenges. Bloomberg L.P. is at something of a crossroads, developing new businesses in the hopes of making it more accessible to a broader consumer audience.
Under Mr. Doctoroff, who joined Bloomberg L.P. just six months before the financial crisis flared in September 2008, the company's revenue has jumped to more than $9 billion, from $5.4 billion. Subscriptions to Bloomberg's signature financial-data terminals — which rent for about $20,000 a year — have grown to 321, 000, from 273,000, despite a shrinking financial sector. With many newsrooms shrinking, Bloomberg has added more than 500 reporters and editors during his tenure.
Still, the company's growth has slowed, particularly abroad. And its news division endured criticism last year in the face of accusations that it withheld a report about government corruption in China to protect its business interests there. Separately, it came under fire after acknowledging that its reporters used the company's terminals to extract subscribers' private information.
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Mr. Doctoroff, who remains a friend of Mr. Bloomberg and will join the board of his foundation, explained his decision to step down: "When Mike decided he wanted to spend some time at the company, and then spent more time, obviously things changed." He added, "It isn't the job I had for the past six years. It's his — he wants to be involved. He doesn't want to consult with me on everything. I get that."
With a wry smile and a laugh, Mr. Doctoroff said: "Mike is kind of like God at the company. He created the universe. He issued the Ten Commandments and then he disappeared. And then he came back. You have to understand that when God comes back, things are going to be different. When God reappeared, people defer."