:Intrusive r:

A feature of many accents of English where a sequence of a non-high vowel and any following vowel is broken up by the insertion of r, even though this r has no historical justification and does not appear in the spelling. An example: The idea of it → ði aɪˈdɪər əv ɪt. Intrusive r may also occur within a word, such as drawingˈdrɔːrɪŋ

See also linking r.