AT&T got its day in court and "the system worked," Stephenson said on "Squawk Box."
"We live in an amazing country," he said. "We have three co-equal branches of government. The checks and balances in this situation worked exactly the way they were designed over 200 years ago."
The $85.4 billion acquisition closed late Thursday, shortly after the Justice Department said it would not apply for a stay of federal judge Richard Leon's ruling that let the deal go forward. However, the DOJ could still appeal the decision even after the completion of the deal.
Stephenson said he's not worried about government retribution, while noting it's been "600 days" since he came on "Squawk Box" to unveil the merger. He's always maintained it was not anti-competitive because it's a vertical integration, meaning the various businesses of both companies don't go head-to-head against each other.
Time Warner's properties include Turner Broadcasting's CNN as well as HBO and the Warner Bros. movie and television studio. AT&T, the nation's second-largest wireless firm, also owns the DirecTV satellite service and offers broadband internet service.
Stephenson said he feels he has all the right people in place to lead the various divisions, and that AT&T plans to invest in the new businesses being brought into the fold.
"We're building a modern media company," he said, though stressing he wants to also preserve the Time Warner culture. "This business we're buying is all about creativity and talent and how can we ensure that we don't disrupt or interfere with that creative ability."
Meanwhile, AT&T will be launching a "very, very skinny bundle" of television programming free to its mobile customers, Stephenson said.
"We will be launching, and you're going to hear more about this next week, a product called 'AT&T Watch TV,'" he explained. "It will be the Turner content. It will not have sports. It'll be entertainment-centered."
AT&T's unlimited wireless customers will get the service for free, he said, "or you can buy it for $15 a month on any platform."
AT&T said in a letter to DOJ officials on Thursday that it plans a "firewall between Turner and AT&T Communications" to prevent improper sharing of information or pricing. Last year, the DOJ sued to block the merger, citing concerns that AT&T could charge rival distributors more for Time Warner content, resulting in higher prices for consumers.
This week's green light for AT&T in federal court was seen as a mandate for other media mergers. And a day after Tuesday's ruling that cleared the way for the Time Warner deal, Comcast announced a $65 billion all-cash bid for the Twenty-First Century Fox assets currently under agreement to be acquired by Disney in a $52.4 billion stock deal.
Stephenson told CNBC on Thursday he's unsure how or whether the AT&T situation should apply to other proposed deals in the media industry. "I don't know how transferable this is to next deal" because the AT&T case was adjudicated on the facts of this particular transaction, he added, echoing judge Leon's ruling.
"The temptation by some to view this decision as being something more than a resolution of this specific case should be resisted by one and all!" Leon said.
During the 2016 presidential campaign, then-candidate Donald Trump said he wouldn't support the AT&T-Time Warner deal. And when he got into the White House, his Justice Department followed through and tried to block it.
Stephenson, an early supporter of Trump, maintained through the legal process that he never tried to curry favor with the president.
The AT&T CEO reiterated on CNBC on Friday that he liked the corporate tax cut and the overhaul of the tax system for individuals that Trump and Republicans pushed through last year. He also said he does not support many of the trade actions by the White House.