"I'm so comfortable here now," Johnson said at a news conference in Allen Park, Mich. "At first, not at all, but being here for five years, being around these people here in Detroit, teammates and just the city -- I'm just growing accustomed to it."
Johnson is scheduled to earn close to $130 million over the next eight seasons, including $113.5 million over the final seven years of the deal, league sources told NFL Network insider Jason La Canfora.
The contract includes $4.5 million in an existing roster bonus that's due on the final year of his rookie deal.
The deal also includes $53 million in guaranteed money, with Johnson's $1.25 million base salary in 2012 guaranteed, and $36 million due in signing and option bonuses. According to La Canfora, $11.5 million in future salary is guaranteed for injury only.
The extension keeps Johnson signed in Detroit through 2019 and reduces his $22 million salary-cap number for the 2012 season, giving the team some wiggle room to add talent through free agency.
"Calvin's one of those guys -- we've said this about a few guys that we have in our building -- whatever they pay him is not enough," Lions coach Jim Schwartz said. "He's truly a special player."
"They were happy to get this thing done with, and I was happy as well," Johnson said. "It wasn't a lot of confrontation. We weren't butting heads or anything. It was just something that we knew needed to get done."
Johnson has 366 catches for 5,872 yards and 49 touchdowns in five seasons, just the sixth player in NFL history to cross 5,500 yards and 45 scores in that span of time.
The Associated Press contributed to this report.