The deal may not be finalized for a day or so pending physicals and paperwork.
"It caught me by surprise," Willis told SI.com from Mexico, where he was vacationing. "I've been on the trading block the last couple of years. I've heard everything. It never affected me. They've asked me for three years if I'm living out of boxes. I haven't been. You have no control over it, and you just try to stay focused."
Willis said that while he loves the Marlins, he's thrilled to join a potential juggernaut in Detroit. "I'm excited to go to the new team," he said. "They're good. I just don't want to go in and mess everything up. I just want to stay on top of my game."
Willis struggled in 2007, when he went 10-15 with a 5.17 ERA after going 58-39 the previous four seasons, including 22-10 in 2005. Some thought the problem was carrying the burden of a losing organization.
"We just didn't play the type of baseball we played the year before," Willis said. "That was my fault. I shoulder the responsibility. There's no excuses. I have to do better."
The Marlins had been close to dealing Cabrera to the Angels but when those talks stalled, the Tigers stepped in.
"If it does happen, obviously they're getting two very good players," said Yankees manager Joe Girardi, who managed the Marlins in 2006. "Miguel Cabrera is one of the finest hitters in the game. He can do so many things with a bat, whether you want him to hit a home run for you, you want to hit and run, work the count, get on base. And Dontrelle Willis has been one of the premier lefties in the National League."
Willis was the 2004 NL Rookie of the Year after going 14-6 with a 3.30 ERA and is 68-54 in his five years in Florida. He has pitched over 200 innings in each of the last three years.
Cabrera hit 34 home runs and knocked in 119 RBIs this year for the Marlins, both career highs. Like Willis, Cabrera has been very durable, averaging 158 games over the last four years.
Detroit had not been considered a contender for Cabrera or Willis.
"It was kind of like, wow, when I heard. I halfway expected one of them to get traded, but not both in the same deal. So it's a little bit of a shock," Marlins left fielder Josh Willingham said. "It's deflating because they're great teammates and good friends. It's going to be hard not seeing them around. I know we got some good players in the deal, but Miguel and Dontrelle are proven big league players, and it's going to be tough to fill those roles. Miguel brings you more than 100 RBIs, 30 home runs and a .300 batting average, and while Dontrelle had a disappointing year last year, he's a workhorse. He's going to eat up 200 innings and he's always healthy. It will be tough to replace those guys."
Cabrera would join an imposing lineup that already includes Magglio Ordonez, Gary Sheffield, Ivan Rodriguez, Curtis Granderson and Placido Polanco. The Tigers also acquired shortstop Edgar Renteria, a five-time All-Star, in a trade with Atlanta this offseason.
"I'm glad we're in the other division," Boston manager Terry Francona said. "That lineup just got scary."
Tigers GM Dave Dombrowski and assistant GM Al Avila originally signed Cabrera out of Venezuela for the Marlins.