One of the oldest record companies. Founded by Edward Lewis.
Had subsidiaries: Brunswick Records, Gennet Records.
Distributed RCA 1957-1971, and Atlantic until 1966.
Became part of Polygram in 1980, which was subsumed by Universal in 1998.
Decca retains the copyright for the names London Records and FFRR, although these are distributed under license by Warner Music Group. (London Records was originally used for US releases only, due to complicated copyright issues).
Chiefly known as classical and jazz label, Decca also had many releases during the rock n' roll era. The label boss famously passed on the opportunity to sign The Beatles, but did have a contract with The Rolling Stones. When the Stones left in the 1970s, Decca declined markedly as a pop music label.
The huge Decca back catalogue is licensed to hundreds of re-issue labels on short-term deals, while original Decca recordings also appear on Verve, Polygram TV and many other UMG imprints.
Note that copyrights expired in Europe (50 years limit) for a good part of the Decca catalog, making it freely available (public domain). This is one of the reasons you now find Decca cuts on many budget/slacky releases (though American copyright holders - the Verve Music Group mainly - still claim rights on these and still - obviously - have control over unreleased material).