The Tigers got reliever Kyle Farnsworth.
The Rodriguez' acquisition occurred on the day that Jorge Posada's 2008 season ended officially because of right shoulder surgery.
The 37-year-old Rodriguez, a 14-time all-star and likely hall of famer, is batting .295 with five homers and 32RBI in 82 games (302 at-bats) this season.
He is in the option season of a $50 million contract.
"It was hard because Kyle was a big part of our bullpen and he loved being here, but we felt that Pudge will really help our club," said Yankees Manager Joe Girardi. "He's been playing very well (and) we're looking forward to him being here."
Posada, also 37, will need 4-6 months rehabilitation time.
Before his surgery, he was batting .268 with three homers and 22 RBI.
In 45 appearances this season, Farnsworth, 32, is 1-2 with a 3.65 ERA.