In formal British English, the noun 'a detail' is always stressed on the first syllable, 'DEE-tale' IPA: /ˈdiː teɪəl/. The same is true of the verb 'to detail'. In America, a quarter of the polulation sampled in 1993 preferred to stress the second syllable in both, 'de-TALE' IPA: /də (or ɪ) ˈteɪl/. This tendency appears to be on the rise.
- You may also like to see AWE's note on the phrase 'in detail'.